NATURAL SCIENCES OF PHILADELPHIA. 295 



epi- and xiphisternal, and one to the discoid entosternal. Hyo- and hyposter- 

 nals united to the disc by suture, and separated from the episternals by a large 

 cartilaginous interval. Head acute, parietal region depressed, frontal slightly 

 arched. Nostrils not subdivided by a transverse process of the septum. Lips 

 greatly developed, forming biangular flaps on each side of the mouth. 



Heptathyra A u b r y i . Cryptopus Aubryi Dumeril. Revue et Magasin de 

 Zoologie; 1856, page 364. 



Total length 2 feet, 6 in.; of sternum 15 in. 6 lin.; of head and neck 11 inches. 

 Numerous specimens from the Fernando Vas river, Equatorial W. Africa. 



The Dogania subplana of India doubtless exhibits the extreme of the 

 Trionychoid modification of the Chelonian type, in the tardiness of the only 

 partial union of the ribs into a carapacial disc, and the imperfect development 

 of the sternal bones. There are but two callosities. Aspidonectes exhibits 

 a superior grade of organization. The union of the ribs is more com- 

 plete, a comparatively small part of their extremities extending beyond the 

 disc in adult age. The sternal bones are better developed, especially the hyo- 

 hypo- and xiphisternals. There are four external callosities. 



Those species which agree in possessing cartilaginous flaps upon the poste- 

 rior lobe of the sternum, are included by M. Dumeril in the single genus Cryp- 

 topus ; but in some respects they are strikingly dissimilar. T. uunctatus 

 and T. Senegalensis are very interesting, as possessing in the free marginal 

 ossicles the analogues of the marginal bones so universal among higher Che- 

 lonians. This far from unimportant peculiarity is wanting in the T. frenatus 

 and P e t e r s i i ; while the additional character of every sternal bone being pro- 

 tected by a corresponding external callosity (their number thus amounting to 

 nine), proves the propriety of the generic name Cycloderma assigned by 

 M. Peters. T. Aubryi, it is seen, agrees with the last in the absence of 

 ossicles, but maintains the more typical Trionychoid peculiarity of one undivided 

 callosity covering the hyo- and hyposternal boues. The extent of the union 

 of these, (hajmapophyses,) with the disc, (pleurapaphyses,) without lateral car- 

 tilaginous or osseous "appendage," offers as good an example of a normal 

 "haemal arch" as is to be found in the order. 



The object of generic nomenclature being, as we understand it, to indicate 

 the modifications of Nature's types and the sensible steps by which they approach 

 each other, to ignore any such step appears to us unphilosophical. Hence we 

 venture to propose for the species under consideration the generic appellation 

 of Heptathyra. 



Aspidonectes aspilus nob. Head acute, plane, not sloping as in Platy- 

 peltis. Lips thin, not developed into flaps. Septum of the nasal orifice with 

 a short process on each side. Ribs eight paira, projecting in the adult about 

 two inches beyond the disc. Disc subcircular, broadly truncate behind, vermi- 

 culately rugose. Vermiculations transverse along the sutures of the costal 

 plates, longitudinal between. Vertebral line slightly depressed. Cartilaginous 

 border extending two inches beyond the edge of the anterior sternal callosity, 

 and 9 in. 10 lin. from the posterior margin of the disc, to within 3 in. 6 lin. of 

 the end of the tail. Sternal callosities four. The posterior subtriangular, 

 anterior, and posterior angles divergent, the inner almost in contact. Anterior 

 angle with an emarginatiou corresponding to an angular process in the posterior 

 border of the hyposternal. The interior and exterior borders of the anterior 

 callosity made nearly right angles with its anterior edge. This is not perfectly 

 transverse, so that the inner borders approach to within 1 in. 11 lin. of each 

 other, they then round off and extend much farther posteriorly than the external 

 borders. Episternal bones small, considerably separated, diverging anteriorly. 

 Claws nearly straight, compressed, sharp at their inner edges, dirty white. 

 Disc brown, vermiculations shaded with yellow. Border, extremities, neck and 

 head dark brown, without spots or markings of any kind. Sternal callosities 

 whitish. 



1859.] 



