394 CRETACEOUS GASTROPODA 
XCVII. EMARGINULA, ZLamarch, 1801. 
1. EMARGINULA sp. (conf. E. GUERANGERI, d’Orb.), Pl. XXVIII, Fig. 8. 
We only possess a fragmentary specimen, and even this devoid of the shell 
surface ; there are, however, radiating, stronger and thinner ribs distinctly traceable, 
the former numbering about 24 on the periphery. The concentric striee are rather 
thin, the slit is anterior and mesial, not extending more than one-third of the 
distance from the edge to the apex, bounded by a raised rib on either side; apex 
excentric, posterior and apparently somewhat incurved. The height and the oval 
shape of the whorl agrees, as likewise do all the remaining characters, with 
@Orbigny’s Hm. Guerangeri, of which two good figures have lately been supplied 
by Guéranger in his “ Album paléontologique de la Sarthe,” 1867, pl. 14, figs. 24 
and 25. It is probable that our Indian fossil is identical with the French species 
occurring in the upper beds of the Gault. 
Locality.—North of Odium, in calcareous, conglomeratic sandstone; apparently 
very rare. 
Formation.—Ootatoor group. 
Order. OPISTHOBRANCHIA. 
Char. Gastropoda with gills situated behind the heart, covered by the mantle 
or exposed ; hermaphrodites ; larve shell-bearing, with two deciduous cephalic fins. 
The OPISTHOBRANCHIA are almost without exception inhabitants of the sea; 
the general form of their body is elongated and nonsymmetrical, in so far as the 
genital organs are almost invariably placed on the right side. The head is distinct, 
provided with two, often thickened, tentacles, and sometimes also with labial lappets. 
The mantle is usually only partially developed on the back, sometimes secreting 
a more or less spiral shell, but not uncommonly the body is quite naked. 
The radula is usually composed of a large number of uniform teeth, of which 
the central ones are occasionally wanting; the stomach is sometimes provided with 
horny plates for the purpose of maceration of the food, the liver generally highly 
developed and sometimes extending into the lateral branches of the body. The 
circulation of the blood is not complete, the auricle of the heart being situated 
behind the ventricle, which receives the blood from behind and sends it to front, 
but the arterian vessels terminate by imperfect canals at the gills. The nervous 
system consists of three well developed pairs of ganglia, being the centres of the 
cerebral system, one providing the mantle and the gills, and the third pair providing 
the foot. The gills are represented by a single or double plume, or by numerous 
plumes; they form in a great measure the basis for farther sub-divisions in this 
order. 
The sexes are always united in the OPISTHOBRANCHIA. The hermaphrodite organ 
is composed, according to the latest researches of Pagenstecher, of a distinct penis, 
being near its tip connected with an inflated vesicula seminalis and a very long vas 
deferens ; there is also @ distinct vagina and a large pyriform receptaculum seminis 
