24s -TERR A NOVA" EXPEDITION. 



(_'</></ i/ii. A diagram of the general disposition of the internal organs is shown 

 in PI. Ill, Fig. 18, to which the following notes may be added : 



Font. The sole of the foot is cleft longitudinally by a shallow gutter surrounded 

 bv a small amount of gland-tissue. Posteriorly, the cleft terminates in a pit whose 

 walls are pleated longitudinally and into which projects a small papilla. The gutter 

 and pit contained a little coagulated secretion, and were surrounded by a considerable 

 mass of gland-tissue, but there was no definite byssus in any of the specimens. In 

 some species of Ciirdifa the byssus is peculiarly strong. 



\i'/T<ntx Si/xf<'in inn! Sense- Organs. The pedal ganglia are coherent but 

 superficially separate, the visceral ganglia completely fused together. There is no 

 abdominal sense-organ, but Spengel's organ upon the root of the branchial nerve is 

 fairly pronounced. 



llt'iirt i aid Ri'iutl OrtjaiiK. The ventricle of the heart is perforated by the rectum. 

 The surface of the auricles, and particularly their internal trabeculse, are richly beset 

 by cells of (apparently) pericardial gland-tissue. Owing to the somewhat imperfect 

 preservation of the tissues, Keber's organ could not be identified with certainty. 



The kidney corresponds in its general structure, in the position of its external 

 orifice, the relations of the reno-pericardial duct, and the position and extent of the 

 intercommunication between the distal arms, with the description and figure of the 

 renal organ of Cardita given by Odhner (8, p. 314). 



Gill*. The gills resemble in their structure those of Cardita (Ridewood, 17, 

 p. 221). 



Gi'iK'i'ufiri' Organ*. The sexes are separate ; the genital duct opens close in front 

 of the orifice of the kidney. The ovarian eggs are surrounded by a thick hyaline 

 capsule, the outer parts of which are dense, the deeper parts vacuolated. In the 

 fresh state no doubt the deeper layers were fluid, and owe their shrunken vacuolated 

 appearance in this prepared material to the action of the reagents used in its 

 preservation. The whole capsule stains deeply with hsematoxylin. 



Although, as a rule, the eggs of marine Lamellibrauchs are practically naked, 

 enclosed at the most in an extremely thin vitelliue membrane, a thick capsule similar 

 to the above is common in fresh-water genera and among the Auatiuacea, and is 

 figured by Deshayes in Cardita cah/<-id<if and in Tri</on<'l/<i (], PI. CVI, Fig. 5, 

 PI. LII, Fig. 7), and described by Loven (5, p. 317) in Cardium pygmceum. 



In one of the specimens examined the eggs had been laid, and were found in 

 masses in the interlaminar spaces of all four demibrauchs. In this position they were 

 closely packed and adherent to one another by the surfaces of their capsules; There 

 seems no doubt that these eggs were lodged in the gills for purposes of incubation, a 

 habit of somewhat rare occurrence among marine Lamellibranchs (14, p. 243), though 



common enough among fresh-water forms. 



