ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 727 



Mollusca. 



New Type of Mollusc* — W. H. Dall describes a remarkable new 

 form of molhise, being a pelecypod or lamellibrancb with an internal 

 shell. 



The animal is about 1 in. in length, somewhat of the shape of a 

 small globose Ci/jyrcea, of inflated ovoid form, translucent, jelly-like, 

 dotted above with small, rounded papillfe, which appear of an opaque 

 white on the general translucent ground. The mantle which covers 

 the dome of the body is tough and thick : the sides are smooth, and 

 nearly free from papillee. The superior median line is a little 

 depressed. The basal part of the anterior end in life is prolonged 

 beyond the general mass in a wide trough, with the convexity up- 

 ward, and somewhat expanded at its anterior extremity. About one- 

 third of the way from the anterior end, the mantle is perforated by 

 an orifice, which pierces it in the vicinity of the mouth. The edges 

 of this orifice project from the general surface, and it is lined with 

 close-set, small papillaB. At about the same distance from the 

 posterior end is another tubular perforation, holding a similar rela- 

 tion to the anus ; which has, however, plain edges, and is not in- 

 ternally papillose. 



Turning the animal over, we find the anterior trough of the 

 mantle prolonged backward, like a slit with plain edges, to about the 

 posterior third ; from this projects a narrow, hatchet-shaped foot 

 with a strongly marked byssus-gland at its posterior angle ; from this 

 a bunch of white byssus extends to the stone or other object to which 

 the mollusc attaches itself. The cavity of the mantle extends some 

 distance behind the commissure of the pedal opening. The anterior 

 point of the foot is roofed by the trough-like expansion above men- 

 tioned. The mouth is provided with two pairs of small palpi. Two 

 gills, very finely microscopically laminate, extend backward from 

 near the mouth, on each side, to the posterior end of the body, the 

 wider one being the inner: between their posterior ends a thin 

 reticularly perforate veil connects the two pairs, and shuts off the 

 anal area from the rest of the mantle cavity. The intestine contains 

 a hyaline stylet, and is considerably convoluted ; but the viscera offer 

 no marked peculiarities when compared with ordinary pelecypods. 

 The shells are enclosed in two little sacs in the substance of the 

 mantle. The umbones are near together, apparently connected by a 

 brown gristle resembling an abortive ligament, and are nearly over 

 the heart. The valves are about 10 mm. long and 1 mm. wide 

 destitute of epidermis, prismatic or pearly layers. There are no 

 muscular or pallial impressions, no adductors, hinge, or teeth. They 

 resemble in form the exterior of Gcrvillia, as figured by Woodward 

 and are pure white. As they lie in the body, they diverge at a rather- 

 wide angle from the beaks, forward. The embryonic valves are 

 retained like two tiny bubbles on the umbones. 



Whatever bo its relations to tho higher groups, a point to be 

 determined by further study, there can be no doubt that the animal 

 * Sciencf, iv. (1884) pp. 50-1. 



