288 PKOCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



Acavidae. With the genera of the Acavidae Trigonephrus agrees, not 

 only in the exceedingly characteristic structure of the lung, but also 

 in having a strong smooth jaw and genitalia without accessory organs ; 

 but it differs from other known genera in the tricuspid teeth. All 

 other forms known to belong to the family have unicuspid or nearly 

 unicuspid teeth, by suppression of side cusps, which many lines of 

 evidence show were present in the ancestral Vasopulmonata. The 

 presence of side cusps in T. glohulm indicates that it is a relatively 

 primitive member of the stock. This conclusion is further emphasised 

 by the fact that, so far as we can judge, the young undergo no such 

 prolonged uterine or intra-oval existence as has been shown to prevail 

 in the typical Acavidae. In this respect, Trigonephrus holds such 

 a I'elation to Helicophanta and Acaviis as typical Achatina bears 

 towards the great West African Metachatinas. 



When the pallial organs of Dorcasia Alexandri and its allies are 

 examined, the relations of that genus to Trigonephr^is may be 

 intelligently discussed. It is likely that Dorcasia also belongs to the 

 Acavidae. In this family the pattern of the lung venation is extremely 

 constant and characteristic, being about the same in genera of Mada- 

 gascar, Ceylon, and Australia. 



Gorilla Humberti (Brot). 



Several specimens submitted by Mr. G. K. Gude, collected by the 

 late Oliver Collett, enable me to confirm the anatomical data obtained 

 by Semper in examining C. erronea, and to add a few further facts. 



The jaw is stout and smooth, arcuate, without a median projection 

 below. 



The radula has teeth according to the formula 19: 19:1: 19: 19. 

 The transverse rows run slightly forward on each side of the middle 

 tooth. All of the teeth are unicuspid, the cusps much shorter than 

 the basal plates (PI. XIV, Fig. 10, a group of central and lateral 

 teeth, and Fig. 11, a group of lateral and marginal teeth). The 

 marginal teeth differ from laterals by the shortening of the basal 

 plates and the elongation of the cusps, which are oblique, broad, and 

 obtuse. The outermost marginals (PL XIV, Fig. 12) are much 

 shortened, without diminution in width. 



The pallial tract (PL XIII, Fig. 3) is long and narrow, and densely 

 pigmented. Scarcely any venation, aside from the pulmonary veins, 

 is visible, even by transmitted light. So plain a lung as this I do not 

 remember seeing in any Helicoid snail. The lung is about 28 mm. 

 long. The kidney is 10 mm. long, about double the length of the 

 pericardium. It is sack-like, with a very large cavity and thin walls, 

 irregularly rugose within, there being a network of anastomosing 

 rugae and lamellae. It excretes through a pore about the middle of 

 the right side (the left side as the lung lies inverted in the figure), 

 without any differentiated ureter. There is no enclosed secondary or 

 gut ureter. 



The genital system (PL XIII, Fig. 1) closely resembles that of 

 Gorilla erronea as figured by Semper. The penis is oblong, stout, 

 and fleshy, contracting into an epiphallus more than three times its 



