NATURAL SCIENCES OF PHILADELPHIA. 187 



IXACANTHUS Cope. 



This genus is similar to tlie next in the cylindric spinous character of the 

 diapophyses af the caudal and lumbosacral vertebraj, but differs from it and 

 all other Delphinidffi with which I am acquainted in the manner of attachment 

 of the epiphyses of the vertebrae. Instead of being nearly plane and thin 

 discs, they are furnished with two oblique faces above, which are capped by a 

 projecting roof formed by the floor of the neural canal, while their central 

 portion forms a knob which fits a corresponding shallow pit of the centrum. 



IXACANTHUS CCELOSPONDYLUS CopC. 



Extremities of centra deeply concave when epiphyses are removed ; length 

 of vertebras less than breadth. 



In. Lin. 



Length centrum lumbar 2 4*5 



Width " " 2 6-5 



Elevation " " 2 4 



Width neural canal on dorsal , 1 



" " " on lumbar 4^ 



Length of caudal vert 2 6 



Transverse diameter , 2 3 



Width diapophysis at base 6 



Lumbar, — elevation of body and spine to anterior zygapophysis 4 9^ 



We have of this species three dorsals, nine lumbo-sacrals and one caudal, 

 one only of the lumbo-sacrals exhibits the spine-lilie diapophysis character- 

 istic of the genus. One of the caudals belongs to an entirely adult animal. 

 The dorsals are rather constricted, and rounded below ; the lumbo-sacrals 

 have a strong median keel, except in one near the canal series, when it again 

 becomes rounded below. 



I first received this species from my kind friend Oliver Norris Bryan, of 

 Charles county, Md. Jas. T. Thoms has also discovered various portions of it. 



PRISCODELPHINUS Leidy. 



Posterior lumbars and caudals spinous, dorsals with flat diapophyses. 



The prominent character of the genus is seen in the lumbo-sacral and 

 caudal vertebrae, whose diapophyses are very narrow at the base, and soon 

 become cylindrical and slender, terminating in an obtuse point. The general 

 form of the vertebrffi is like those of Delphinus, but with the exception above 

 noted, that the caudal vertebrae, instead of being shorter than the dorsals, are 

 really longer, till we approach the posterior portions of the series. The largest 

 of the typical species will not exceed seven feet in length, while the aberrant 

 P. flagellator has been perhaps twelve. 



Tn the P. spinosus Cope, the spinous form of the diapophyses is exhibi- 

 ted among the longer ones of the lumbar series considerably in advance of the 

 caudals. In P. atropius Cope, and P. c o n r a d i Leidy, I have seen it on 

 the most posterior lumbars only, though it may occur further anteriorly, and 

 several such have the diapophyses much narrowed. I have not seen it in 

 theP. harlani Leidy, but it probably exists there, as the species is very 

 near the P. c o n r a d i. 



Priscodelphinus spinosus Cope. 



This species is represented by two cervical, three dorsal and eight lumbo- 

 sacral vertebrae ; they are about as broad as long, with articular faces trans- 

 versely oval. As thev belong to more than one individual they vary a little 

 jnore than is to be expected in a single series. They differ of course greatly 

 in the size of the neural canal, with the position in the column. That with 

 the smallest, (the posterior) exhibits no zygapophyses or their rudiments. 

 General form depressed ; sides of centrum nearly plane to a well-marked 

 obtuse median keel. 



1868.] 



