NATURAL SCIENCES OF PHILADELPHIA. 



polluted with mud, they are marked on each scuta with diverging or radiating 

 lines of dnrker. 



I have not adopted Mr. Agassiz's name in describing this animal, as I do not 

 think that his arrangement of Kinosternoids founded on a proper basis. If I 

 were to adopt his classification, I should describe three of his genera as follows, 

 premising that I think it is offering a violence to nature to separate the two 

 first. 



KlNOSTERNUM. 



Sternum entirely closing up the box of the shell, with eleven scutae and eight 

 bones, there being no entosternal, but the whole piece may be divided longitu- 

 dinally from front to rear into two pieces, which are afterwards subdivided. 

 The sternum is bilobed, each lobe moveable from the side of the abdominals on 

 the posterior joint of the hyosternals and the anterior of the hyosternal bones. 

 By closing the two lobes it is enabled to cover entirely the head and limbs ; 

 the posterior lobe being as wide as any part of the sternum, there can be of 

 course but very small wings by which it is attached to the carapace. In fact 

 they are scarcely perceptible. The upper jaw is most frequently hooked and 

 the tail armed with a nail. 



Thyrosternum. 



This genus differs from the preceding in the shape and mode of attachment 

 of the sternum to the carapace, the number of bones and of scutae is the same, 

 but the wings are much longer; it has likewise two moveable lobes, the anterior 

 attached by suture at the sides and by ligament in the centre ; the posterior 

 one entirely by suture, both of them narrower than the opening of the carapace, 

 particularly the posterior one ; consequently the animal is not able to with- 

 draw its softer parts entirely from view. It is always emarginate behind, the 

 upper jaw is almost always hooked, and the tail generally armed with a nail. 

 The transitus from Kinosternum to Thyrosternum is so perfect, that it becomes 

 difficult in some instances to say to which genus a specimen belongs. 



Ozotheca. 



Sternum very much shorter and narrower than in the other two genera, con- 

 stituted in the same manner, but the gular plate is generally very small. It is 

 jointed like the others both before and behind. The upper lobe is quite movea- 

 ble, but the lower little so, inasmuch as the fourth scuta projects somewhat 

 beyond the suture connecting this part with the abdominals, but there is a wide 

 space above it filled with ligamentous matter, which allows of some degree of 

 motion. This joint early in life becomes immoveable. The anterior joint in old 

 animals is apt to become permanently soldered to the adjoining bone. The 

 wings are longer and uarrower than in the others. 



The following characteristics are common to all these three genera. The 

 chin is furnished with two or more small warts, and the feet have some folds or 

 large scales, the fore feet on the anterior side, the hind feet on the posterior. 

 They all have a strong musky odor. 

 ' Although it may appear perfectly proper to separate the last genus from the 

 two others, yet in Wagler's K. hirtipes a very near approach is made to 

 Ozotheca, it has a very narrow sternum, emarginate behind and the branchial 

 plate is quadrangular, very much resembling what we see in 0. odo?-ata, the 

 jugular scuta is large and triangular, the upper jaw hooked, and the tail ungi- 

 culate ; in these three particulars exactly like the T. Pennsylvanicum. In the 

 young of the 0. odorata it is impossible to distinguish the sternum from that of 

 the T. Pennsylvanicum, except by the form of the brachial scuta ; it is very 

 remarkable, however, that the first which in the adult state has the nuchal scuta 

 small and irregular in shape, when very young has it very large and perfectly 

 triangular. The most of the Kinosterna and Thyrosterna have the tail armed 

 with a nail. Whether any of the Ozotheca are thus furnished I do not know, 

 never having had an opportunity of examining more than two species (unless 

 Wagler's K. hirtipes is admitted to be one). Should one, however, be found 



1859.] 



