likely that the wings of this bird were more efficient than those of the ratites on account of the apparently welldeveloped remiges.

COLYMBI

Definition.-Oil gland tufted. Aftershaft present. Aquincubital. Accessory semitendinosus absent. Biceps slip present. Gluteus maximus large, extending behind acetabulum. Ceca long. Skull holorhinal, without basipterygoid processes, schizognathous. Tibial crest strongly developed.

This group of birds contains two very well-marked families, the divers (Colymbidæ) and the grebes (Podicipedidæ). In view of their numerous and important points of similarity I have not thought it desirable to separate these two families quite so widely as has GADOW. The Colymbidæ contain but one genus, Colymbus, with four species. Of the grebes there is perhaps also only one well-marked genus, Podicipes. But the Central American Centropelma (of SCLATER and SALVIN) has some claims, on account of the complete loss of flight, to generic distinction, while in the course of the following pages it will be seen that there are certain, if small, reasons for distinguishing Echmophorus and Tachybaptes. Podilymbus, another alleged genus, has not been dissected.

Our knowledge of the anatomy of this group of birds is chiefly due to NITZSCH,' BRANDT,2 COUES,3 SHUFELDT, and myself."

As to external characters, there is a close agreement among the Colymbi. The number of rectrices in Columbus glacialis I find to be twenty. NITZSCH gives eighteen to twenty for the genus. Specialised rectrices are not recognisable among the grebes. The inferior tract of feathers is

Loc. cit.

2 Beiträge z. Kenntniss d. Naturg. d. Vögel,' Mem. Ac. St. Petersb. 1840, p. 197.

3 On the Osteology of Colymbus,' &c., Mem. Bost. Soc. Nat. Hist. i, 1866, p. 131.

46 Concerning the Taxonomy of the N. American Pygopodes,' &c., J. Anat, Phys. 1892, p. 198.

5 Notes upon the Anatomy of a Grebe (Æchmophorus major),' &c., P. Z. S. 1896, p. 538.

divided into two about halfway down the neck; the two tracts are not again divided upon the trunk, where they are broad. The spinal tract divides high up on the nock (Podi2 ceps cristatus) or only between the shoulders (Colymbus glacialis). The anterior part of the spinal tract is stronger than the posterior part, and is separated from it; the latter is solid, enclosing no space.

The patagial tendons of Colymbus glacialis are rather simple. The tendon of the brevis is a rather broad undivided band. There is no patagial fan, but, as in Echmophorus, a delicate tendon arises from the fore arm near the insertion of the tensor brevis and ends in the biceps slip. In Columbus arcticus, according to FÜRBRINGER'S sketch, a broad diffuse tendon arises from biceps slip, and ends freely upon the patagium. The first description given is from my own dissection of C. glacialis, and agrees with a manuscript note of Mr. FORBES upon C. septentrionalis. But C. glacialis apparently sometimes approaches C. arcticus. I have a manuscript sketch by Professor GARROD showing a broad band of fibres arising from the biceps slip, but ending on the fore arm.

The anconaus has a humeral head. The expansor secundariorum appears to be absent. The biceps is single-headed. The leg muscle formula, in contradistinction to what we find in the grebes (where it is BX-), is ABX+.

There is a peculiarity in the gastrocnemius of C. septentrionalis which is worth calling attention to: one of the heads of that muscle arises from the tendinous end of the gluteus maximus.

The femorocaudal is tendinous for half its length; its accessory is a very large muscle. The ambiens in Columbus glacialis has two heads of origin.

The combined plantar tendons give off a small slip to the hallux in C. septentrionalis, as in Podicipes minor.

The divers have two carotids, the more modified (cf. leg formula) grebes only the left.

The lobes of the liver in the Colymbi are equal, and there is a gall bladder.

The following are a few intestinal measurements :

The cæca of C. septentrionalis are conical and saccular in form, with irregular but distinct transverse rugæ.

The syrinx in the divers (Colymbus septentrionalis) is not in any way remarkable in form. The last tracheal rings and

the first bronchial are ossified and firmly attached to each other. The pessulus is also ossified. The succeeding bronchial rings are soft and cartilaginous. The powerful intrinsic muscles are inserted partly on to the last tracheal ring and partly on to the first bronchial, the line of insertion being oblique.

The syrinx of Echmophorus (fig. 188) has a very incomplete bronchidesmus, a very wide space between the two bronchi existing above its anterior edge. The last two tracheal rings are fused to form a long box, into the composition of which it appears to me that the first bronchial semiring enters. In any case, if that be not so, the first bronchial

semi-ring has the unusual relations shown in the drawing, which are perfectly consistent with the belief that the ring is the second bronchial. The intrinsic muscles are attached to the third tracheal ring in front of the tracheo-bronchial box. The bronchial semi-rings are fairly ossified, but have rather wide membranous interspaces.

In Podicipes cristatus there is the same failure of the intrinsic syringeal muscles to reach even the end of the trachea. A box is formed by fusion at the end of the trachea, into which it appears to me the first bronchial semi-ring does not enter. The bronchial semi-rings are deeper and closer together, and the whole bronchus is more ossified, than in the last genus. The bronchi, too, are longer.

In Podicipes cornutus the syrinx is much the same, but of course smaller. The first free semi-ring of the bronchus seems to be No. 2. There is a wider membranous interval between it and the antecedent tracheo-bronchial box than in the last species.

Tachybaptes fluviatilis (fig. 189, p. 388) has a different syrinx. The last three tracheal rings are only fused in front, though they are closely united laterally. These rings are much ossified. The insertion of the intrinsic muscles is remarkable. They run obliquely forward, converging, to be inserted into the last three tracheal rings. The first bronchial semi-ring is arched, and ossified in front, where it is fused with the tracheal box; otherwise it and the succeeding rings are cartilaginous. It is clear, therefore, that the syringeal characters justify the generic distinction here adopted.

1

The cervical vertebræ are more numerous in the grebes than in the divers; they are only fourteen or fifteen in the latter, twenty-one in Echmophorus and Podicipes cornutus. Cervical vertebræ 10 to 16 in Echmophorus have a catapophysial canal; on 17 and 18 the hypapophyses are blade-like and enormous; these processes extend to the very end of the dorsal series. The last cervical and the first three dorsals are fused. There is no catapophysial

A canal is nearly formed in Podiceps.

canal in Colymbus; but the hypapophyses are greatly developed, and in the dorsal region Y-shaped, with widely divergent flattened and expanded limbs. None of the dorsal vertebræ are fused. Six ribs reach the sternum in the two grebes mentioned; eight or nine in the divers. The sternum is one-notched; in the grebes it has in addition a median triangular notch. There is no anterior spine to the sternum in the grebes. The procoracoid is moderately large and hooked in the divers, absent in grebes. The pelvis is very elongated and compressed, as in Hesperornis, but the ischia are not free from the ilia, as in that bird.

In the skeleton of the leg the most conspicuous feature is the highly developed cnemial crest. The patella too is very large in the grebes, but not in Colymbidæ, where, indeed, it is not ossified. In these particulars the grebes resemble Hesperornis. The principal skull characters have been already mentioned in the definition of the group. In addition to these matters the strongly marked temporal fossa may be mentioned, which nearly meet on the upper surface of the skull. They are not so well marked in the small Podicipes minor. In the divers are strongly marked furrows for the supra-orbital glands; this is not the case with the grebes. The former have also a single median occipital foramen above the foramen magnum. The ectethmoids exhibit the bullate form so characteristic of the Anseres.

It may be useful to state in a tabular form the principal characters of the grebes and divers.'

These characters appear distinctly to point to the more modified structure of the grebes. There are reasons (p. 165) for regarding a small number of cervical vertebræ and a

The extinct Colymboides (C.minutus, M.-Ed.; C. anglicus, LYDEKKER), Of which the former is known by a humerus, the latter by a coracoid, and possibly a piece of sternum, is said to combine the characters of grebes and divers.