24G "TERRA NOVA" EXPEDITION. 



;i""Tration of scattered muscle-fibres, situated in the body- wall in the neighbourhood 



DO D / O 



of the ventral extremity of the hinge. 



The foot shows upon its ventral surface a shallow byssal cleft, which deepens at its 

 posterior extremity to form a pit occupied by from 8-10 longitudinal laminae, 

 surrounded by a considerable depth of glandular tissue. There is apparently, however, 

 no byssus. 



*\'i'i'roi<3 Si/xti'iii and Sense- Organs. In conformity with the relatively great 

 length of the body, the visceral and cerebral ganglia lie at some distance apart, and do 

 not show the remarkable concentration towards one another that has been described by 

 Pelseneer (15, p. 874) in certain species of Lima. The cerebral and pedal ganglia are, 

 on the other hand, closely approximated to one another, united by short stout 

 connectives. 



The otocvsts are large, and lie behind the cerebro-pedal connectives. 



Digestive (h-t/anx. The mouth opens freely to the mantle-cavity between the lips, 

 and is not shut in, as in many species of Lima (Pelseneer, 13, p. 722, and 16A, p. 34), 

 by the fusion of the lips in front of it. The stomach, as in L. hians, lies mainly in the 

 left umbo. 



The intestine occupies the position shown in Fig. 16, forming a simple S-shaped 

 coil which, in its forward bend, passes to the right of the stomach and thence bends 

 backwards between and below the two lateral chambers of the pericardium and divisions 

 of the heart, and above the hinder connecting passage of the pericardium (Fig. I6,pc.c.) 

 to reach the upper surface of the adductor. 



Han't. Owing to the great breadth of the dorsal surface of the body, the heart 

 and pericardium are drawn out to either side, as in many of the Arcidse. The heart is, 

 in fact, completely separated into two lateral halves, each consisting of a single ventricle 

 and auricle. In front, each ventricle is continued forward as a fine aortic vessel 

 beneath the floor of the anterior extremity of the pericardium, and may possibly form a 

 connection through this vessel with that of the opposite side. 



No actual passage from one ventricle to the other was, however, satisfactorily 

 traced, either by sections or dissections, and if present it must be exceedingly minute. 

 In L. hit tns the ventricles, though widely separated laterally, are in communication, 

 close in front of the adductor, by a connecting channel, which, though narrow, can yet 

 easily be traced even by dissection. 



The pericardium conforms to the shape of the heart, but posteriorly the two lateral 

 chambers into which it is divided communicate beneath the rectum by a narrow channel 

 (Fig. 16, /"'''.) Pericardia] gland-cells are freely distributed upon and within the 

 auricles. 



Jii'inil ni//! Generative Oryim*. The renal organs (Fig. 16, r.) are saccular, and 

 occupy a position beneath the pericardium from a short distance behind its anterior 

 extremity to the autero-ventral face of the adductor, having thus a much greater autero- 

 posterior extent than in the species of Lima described by Odhuer (8, p. -307). 



