294 CATALOGUE OF THE SPECIES OP VERTEBRATA FOUND IN THE 



vated as in the D. incisious, but they are moi'e robust, and have transverse processes 

 or branches which resemble the yard-arms of a ship's mast. In a full-sized individual, 

 the longest cross-arms, which are the lowest in position, have an ex^janse of two hun- 

 dred and sixty millimeters, or ten and a quarter inches, while the spine has about the 

 height of five hundred millimeters (19.75 inches), the body being 60 mm. long. The 

 animal must have presented an extraordinar}' appearance. Perhaj^s the yard-arms 

 were connected by membrane with the neural spine or mast, thus serving the animal 

 as a sail, with which he navigated the waters of the Permian lakes. 

 The thi-ee sj^ecies of Kaosaurus differ as follows: 



I. Neural spines distally cylindric. 



Distal transverse processes represented by tuberosiiies, iV, cruciger. 



II. Neural spines distally dilated and compressed. 



Palatine teeth small, widely spaced, iV. elamger. 



Palatine teeth large, closely packed, N. microihis. 



The skull. — One of the best preserved skeletons of the iV". claviger includes a skull, 

 but the extremity of the muzzle is unfortunately wanting. The median line rises for- 

 wards so that the convexity of the top of the muzzle is higher than the posterior parts 

 of the skull, whose profile descends rapidly. This throws the orbit far back and gives 

 the animal a peculiar appearance. 



The orl)it is nearly round, the superciliary border being arched. Anterior to it 

 is a large anteorbital fossa bounded by a longitudinal ridge above. Above the'ridge 

 is a longitudinal groove, which is separated from that of the opposite side by a narrow 

 ridge only. The quadrate bone is large and laminiform, and is truncate above, having 

 a good deal the shape of the corresponding bone in a fish. The parietal buttress is 

 produced downwards and backwards, and is in contact with the superior third of its 

 posterior border. Beneath and within it is a narrow opisthotic. The pterj^goid is 

 largo, and is distally vertically compressed. Anteriorly it becomes flattened so as to 

 be horizontal, and is studded with small conical teeth rather distantly placed. 



The transverse series of palatine teeth on a massive Z-shaped bone, seen in the 

 D. inciswus, is not preserved in this specimen, but the explanation of the structure is 

 furnished by a specimen of the Dimetrodon semiradicatus Cope, of which a second 

 specimen has been found by Mr. Cummins. Here the palatine bones with their teeth 

 are preserved. They are not so massive as in the D. incisivus. Posteriorly they jjass 

 into the longitudinally flattened i)art without interruption by suture, so that I suspect 

 that this part is to be rel'erred to the palatine rather than to the pterygoid bone. It 

 is studded with small teeth, but they are not nearly so numerous as in the N. cruciger. 



