MORPHOLOGICAL REVISION 



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sessile in the last two, in which the rudimentary ribs seem to be anchylosed 

 to their extremities. 



"Atlas: The atlas was preserved in this specimen in place. It is some- 

 what eroded and does not seem to differ from a better preserved specimen 

 belonging to the closely related genus Dissorophus, which I have figured in 

 plate 23, fig. 1 1. This vertebra seems to be a single element, though doubtless 

 it is composed of coalesced hypocentrum and neurocentra; but I can dis- 

 tinguish no sutural lines. The anterior surface shows two facets for articu- 

 lation with the occipital condyles. On the posterior side the body has a 

 deep concavity, pierced above its middle by a small notochordal foramen. 

 The neuropophyses are simple processes, of nearly uniform width, and 

 flattened; they lie closely in apposition with the sides of the spine of the 

 second vertebra. The same condition is found in Eryops and Trematops, and 

 is doubtless the usual structure of the atlas in the rhachitomous amphibians. 

 Back of the neurocentra I find no articular surface for the attachment of 

 the pleurocentra, though the anterior border of the next vertebra seems to 

 indicate the presence of small pleurocentra. 



"Sacrum: In Cacops we have two well-developed pairs of sacral ribs 

 broadly attached to the ilia. Of these, the first pair is a little larger and 

 stouter than the second, though differing otherwise but slightly. The stout 

 vertebral ends have two articulations, with a small non-articular surface 

 between them, the upper and larger one attached firmly to the neurocentrum, 

 the lower to the upper border of the hypocentrum, which again presents 

 a parapophysial protuberance for its union. The somewhat crushed con- 

 dition of the arches of the sacral vertebrae, as they were found lying in the 

 pelvis, prevents the determination with certainty of the relations of the 

 neurocentra to the hypocentra, but I suspect that they articulate on the 

 sides with the ribs only and not with the hypocentrum. Beyond the artic- 

 ular head the stout shaft of the ribs is constricted for a short distance into an 

 oval form, and then suddenly expands into the large flat or outwardly con- 

 cave portion for union with the ilium. This thinned expansion of the first 

 rib has an emargination on the upper posterior border, in which fits loosely 

 the lower anterior border of the second rib, the two forming an elongated, 

 nearly plane surface, which extends the whole length of the lower part of 

 the ilium in its greatest width nearly opposite the upper part of the acetabu- 

 lum. The first sacral hypocentrum is rather larger than the preceding one, 

 with a parapophysial facet at each side for the rib. The second hypocentrum, 

 of nearly equal size, has also a like facet for the rib on each side. The neuro- 

 centra of these two vertebrae are in part missing, apparently due to some 

 accident before fossilization. 



"Tail: The tail was preserved complete, but the flattened end was 

 sHghtly dislocated, doubtless due to its thin, compressed form. The small 

 bones of the neural side of the first six, or pygal, vertebrae were so small and 

 so confused in the matrix that not much could be made of them. The_ six 

 pygal hypocentra were found attached in a continuous series. There is a 

 slight, very slight, possibility that an additional one may have been lost in 

 the matrix at the place where the dislocation occurred, but I think not. The 

 tail could not have been more than a fourth of an inch longer or shorter than 

 is shown in the restoration. The first six, or pygal, hypocentra decrease 

 rapidly in length. With the fifth is a short, rudimentary rib, a mere pointed 

 tubercle, and several similar ribs were found loose in the matrix. 



