136 Zoological Society. 



the part anterior to the tentacles being produced in the form of a 

 proboscis, equalling in length the whole body behind it, and termi- 

 nated by a clavate extremity. The tentacles or antennae are of pro- 

 portional length, reaching, in some specimens, to the beginning of 

 the terminal expansion of the proboscis. The second external cha- 

 racter is a moderately long subcompressed process, projecting for- 

 wards between the head and the anterior margin of the foot, like a 

 second head, but consisting only of a soft duplicature of the mantle, 

 with muscular fibres for protraction and retraction. In some speci- 

 mens the apex of this process was expanded and a little produced on 

 each side. 



" The foot, in the specimens examined, was much smaller in pro- 

 portion than in Calyptrcea or Calypeopsis ; it presents a subcircular 

 form, as in Cal. Sinensis, but only equals half the diameter of the 

 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 Calyptraidce. In these the branchiae 

 consist of a single series of simple, elongated, close-set and very 

 numerous filaments, extending along the left side of the body in 

 Calyptraa Sinensis, and making the tour of the mantle in the Caly- 

 peopsis. In Lithedaphus the Ijranchise 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- 



* It is here described as contracted in specimens preserved in spirit, the 

 specimens of Ccdijpfrcea and Calypeopsis compared witli it being in the 

 same state. It is, doubtless, expanded in the living animal, as a thin, mus- 

 cular and secreting disk over the basal plate. Aluch sharp criticism has 

 been expended on the genus Gastroplax, De Blainville. It was founded 

 in error, no doubt ; but future conchologists, who may he 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. 



