ANATOMY OF A COLLECTION OF SLUGS FEOM N.W. BORNEO. 305 



semiuis opens. This is an irregular-shaped sac with a short duct. The penis is a 

 thick, muscular-walled tube, narrow at its proximal end, but increasing in size as it 

 nears the distal end, where it makes a sharp bend to the right, this distal extremity 

 forming a sac-like extension (PI. II. fig. 34, 35). On the left-hand side is a loop- 

 like extension — the Henkel of Simroth. The vas deferens leaves the distal extremity 

 of the penis on its ventral side (PI. II. fig. 36, v.d.). The retractor muscle also is inserted 

 on the ventral side, at the point where the penis makes a sharp bend to the right, 

 (PI. II. fig. 36, r.m.). The dart-gland (PI. II. fig. 34. d.gl.) is a large, muscular organ ; 

 distally it presents a swollen appearance which occupies about one-half; the proximal 

 half is tube-like. 



Compared with the three known species of Collingea, viz., C struhelli, Simr., 

 C. pollonerai, Cllge. and Godw.-Aust., and C. simrothi, Cllge. and Godw.-Aust., this 

 species approaches most nearly to C. simrothi. It differs considerably from C. strubelli 

 (12) in the form of the penis and dart-gland, and in the same manner from C. pollonerai. 



VT. The Genus Isselentia, n. gen. 



Animal slug-like. The mantle anteriorly forms two wing-like appendages lying on 

 each side of the visceral mass, inner borders plicated or folded, comes up around the 

 posterior and lateral borders of the visceral mass ; shell-borders thin. Dorsum 

 posteriorly keeled. Generative orifice behind right lower tentacle. Small caudal mucous 

 pore. Foot-sole divided into median and lateral planes. Viscera elevated into the dorsal 

 hump, the body-cavity not extending beyond it into the tail, which is solid. 



Generative system : penis with or without diverticulum. Sessile receptaculum 

 seminis. Dart calcareous, with small laterally placed aperture. 



1. Isselentia plicata, n. sp. 

 PI. II. figs. 13-156 ; PI. III. figs. 37-49. 



Animal yellowish with dark blue dorsum posteriorly, head bluish. Mantle reddish- 

 yellow, with small blackish spots and blotches ; shell-border thin. Posterior portion of 

 dorsum exhibits a wavy keel of a deep yellow colour. Rugse more or less ovoid. 

 Caudal mucous pore small and partly hidden by the extremity of the dorsum. Peripodial 

 groove very prominent. Foot-fringe yellow, with fine, very closely set lineoles. Foot- 

 sole yellowish, divided into median and lateral planes. 



Length (in alcohol) 26 millim. 



Shell amber-coloured ; a thin membranaceous sac ; apical whorl distinct. 



Hob. — Mt. Penrissen and Mt. Santubong. 



Generative Organs.— (PI. III. figs. 37-49.) 



The penis is of considerable length ; it has a somewhat globose proximal portion, 

 followed by a narrower portion, again expanding and narrowing, and terminating by a 



