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entire body* ; its whole margin is free, not produced anteriorly into 
lobes, as in Calypeopsis. The dorsal surface of the mantle is im- 
pressed with a deep horse-shoe fissure, receiving the internal plate 
of the upper shell. The aperture of the branchial chamber extends 
transversely across the back of the head, but conducts to a cavity of 
unusually small extent. The contained breathing organs differ not 
merely in relative size, but likewise very remarkably in structure, 
from the previously dissected Calyptreide. In these the branchiz 
consist of a single series of simple, elongated, close-set and very 
numerous filaments, extending along the left side of the body in 
Calyptrea Sinensis, and making the tour of the mantle in the Caly- 
peopsis. In Lithedaphus the branchie consist of two short parallel 
rows of conical, subcompressed, plicated vascular processes, twelve 
to fourteen in each row, and limited, like the branchial cavity, to the 
anterior part of the dorsal aspect of the body. The heart, lodged in 
a wide pericardium, and consisting of a large auricle with thin, sub- 
transparent walls, and a small, opake, conical ventricle, is situated 
at the left extremity of the branchial chamber, receiving the branchial 
veins, and sending its largest artery to the ovarium, which, in the 
specimen dissected, formed the left portion of the visceral mass. 
The oviduct, at first slender and convoluted, expands on the right 
side, where it is disposed in three long folds, which were laden with 
unusually large elliptical ova. At its termination, close to the 
branchial orifice, there is an oval mucous gland, and a short conical 
filament projects from the inner surface of the mantle. The proboscis 
is surrounded by a thick muscular tunic, inclosing a long, rasp- 
like, horny tongue, and at its base are two simple salivary follicles. 
‘The cesophagus expands into a small stomach, imbedded in a follicu- 
lar liver. “The intestinal canal is more complicated than in Calyptrea 
or Calypeopsis; it bends towards the left side, and there forms a 
small mass of double spiral coils, five or six in number, from which 
the rectum is continued along the floor of the branchial chamber, in 
the interspace of the gills, to the outlet of that chamber on the right 
side of the neck. 
«The nervous system is chiefly distinguished from that of the Ca- 
lypeopsis by the larger relative size and closer approximation of the 
supra-cesophageal ganglions, which here equal the inferior masses. 
Besides the chords connecting the upper with the lower ganglions, 
the upper ganglions give off each three nerves: the largest runs 
forward in a zigzag course to the clavate mouth; the second supplies 
* It is here described as contracted in specimens preserved in spirit, the 
specimens of Calyptrea and Calypeopsis compared with it being in the 
same state. Itis, doubtless, expanded in the living animal, as a thin, mus- 
cular and secreting disk over the basal plate. Much sharp criticism has 
been expended on the genus Gastroplax, De Blainville. It was founded 
in error, no doubt; but future conchologists, who may be tempted to cast a 
reflection on its author, should remember that he has rendered services to 
Conchology such as few can hope to rival, and will do well to bear in mind, 
that the secretion of a shelly valve by the foot of a gastropod is not only a 
possibility, but is a reality in nature. 
