NATURAL SCIENCES OF PHILADELPHIA. 295 
epi- and xiphisternals, and one to the discoid entosternal. Hyo- and hyposter- 
nals united to the dise 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 Anubryi. Cryptopus Aunbryi Dumeril. Revue et Magasin de 
Zoologie; 1856, page 364. 
Total length 2 fect, 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 
@ superior grade of organization. The union of the ribs is more com- 
piete, 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. punctatus 
andT. 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 
andPetersii; while the a:ditional character of every sternal bone being pro- 
tected by a correspording ex'ernal 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 maiutains the more typical Trionychoid peculiarity of one undivided 
callusity covering the hyo- and hyposternal bones. The extent of the union 
of these, (haemapophyses,) with the disc, (pleurapaphyses,) without lateral car- 
tilaginous or osseous “appendage,” offers as good an example of a normal 
“hemal arch”’ as is to be fuund 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 
ven'ure to propose for the species under consideration the generic appellation 
of Heptathyra. , 
Aspidonectes as pilus 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 pairs, projecting in the adult about 
two inches beyond the disc. Disc subcircular, broadly truncate bebind, vermi- 
culately rugose. Vermiculations transverse along the sutures of the costal 
plates, longitudinal between. Vertebral lineslightly 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, 
auterior and posterior angles divergent, the inner almost in contact. Anterior 
angle with an emargination 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 pertectly 
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, coasiderably separated, diverging anteriorly. 
Claws nearly straight, compressed, sharp at their inner edges, dirty white. 
Dise brown, vermiculations shaded with yellow. Border, extremities, neck and 
head dark browu, w.thout spots or markings of any kind. Sternal callosities 
whitish. 
1859.] 
