2'10 "TKRRA NOVA" EXPEDITION. 



(Fig. 9 A, m.c'.) and from the point jit which liotli dernibranchs become attached to the 



liody still continues backwards (Fig. ( Ju, /.'.), burrowing beneath the integument 

 above the kidney nearly to the level of the adductor (Fig. !)o, m.c.). A similar 

 supra-branchial extension of the mantle-cavity occurs, as will be mentioned later, in 

 Philobrya. 



In one of the specimens examined a number of eggs had been extruded, and were 

 lying in the mantle-cavity in front of and between the gills.* The eggs were loaded 

 with yolk-granules of remarkable size, and were surrounded by a very delicate vitelliue 

 membrane, in striking contrast to the heavily encapsuled eggs of Venericardia and the 

 Auatinacea mentioned below. 



3. Area (Barbatia) sp. 



Station 36. Two specimens from a rock-pool in South Trinidad. 



The animal in all essential particulars shows the type of structure characteristic of 

 the genus Aim. 



The byssal apparatus is strongly developed, and, as in other Areas in which this 

 is the case, the posterior retractor pedis is enormous, and dominates the arrangement 

 of the other soft parts in its neighbourhood, crowding the heart and the main part of 

 the pericardium forward, and separating the hinder part of the kidneys and pressing 

 them downwards into the upper part of the gill-axis. 



Another factor that exerts great influence upon the form of the heart and peri- 

 cardium in most species of Area is the great breadth of the body between the umboues. 

 In the species under review this region is very broad, and the heart and pericardium 

 are stretched transversely, separating both into distinct and disconnected halves, 

 except for an extremely narrow communication between the anterior extremities of 

 the ventricles. The walls of the two pericardia! chambers are united to this transverse 

 ventricular connection, but the chambers themselves show uo open communication with 

 one another. 



The passage between the auricles and ventricles is guarded by valves, and not 

 merely by a sphincter muscle as described by Matthias (6, p. 422) in A. (Barbatia) 



The rectum, in passing from the visceral mass to the upper surface of the adductor, 

 lies below and behind the connection between the two ventricles, a position common to 

 many species of Area, though not universal throughout the genus. 



Nernitix System and Sense- Organs. The nervous system shows lateral concen- 

 tration of both the visceral and the pedal ganglia. The abdominal sense-organs are, 

 as usual in the genus, well developed ; the otocysts are relatively small, oval in shape, 

 and situated slightly above and to the outer side of the pedal ganglia. 



* Incubation, though as a rule rare amongst marine Lamellibranchs, is stated by Pelsenecr 

 ( 1 1 , p. 101) to be characteristic of many Antarctic species. 



