624 NOTES ON PROSOBRANCHIATA, 



the dorsal as the superior, and the ventral as the inferior aspects 

 of the mollusc. 



The mantle is thin and transparent; through it may be seen, 

 beginning from the left, the osphradium, branchiae, mucous gland, 

 rectum, and the uterus or vas deferens. Immediately posterior 

 to the pallia! cavity, and slightly to the left lies the nephridium. 

 Below, posterior to the columellar muscle, the posterior oesophagus 

 and anterior aorta may be seen through the thin connective wall, 

 between the body and visceral coil. The genital gland lies over 

 the superior surface of the visceral coil, covering the liver which 

 constitutes the greater part of the coil; inferior!}' the stomach 

 may be seen. The branches from the aorta visceralis reticulate 

 over both surfaces, but more profusely on the superior. Along the 

 axis of the coil, for about half the length thereof, the posterior 

 oesophagus may be seen; the main trunk of the aorta visceralis is 

 also situated here, but extends to the end. 



The osphradium (PI. xxx., fig. 2, osph.) is extremely simple; a 

 very narrow thread of epithelial tissue, nearly as long as the 

 branchiae, without any pectinations whatsoever; as already stated, 

 it is but slightly innervated. 



The branchice (fig. 2, cten., and fig. 5) are more simple than in 

 Littori^ia, the filaments being shorter and narrower. The tine 

 thread-like prolongations found in that genus, Lotorimn, Natica, 

 etc., are here absent. These prolongations should, I think, be 

 regarded as venous sinuses rather than as part of the ctenidium. 

 In the species under consideration a large lacuna (fig. 5, /.) may 

 be observed defining the anterior distal half of the organ. This 

 is provided with such definite walls that it might well be regarded 

 as a vein. 



The mucous gland (fig. 1, m.gl.) is normally large; it lies along- 

 side of the rectum, to the left, and starting a little behind the 

 anus continues back to the end of the pallial cavity. It is of a 

 grey colour, and consists of large cells of concentric structure. 

 During fecundity the uterus, the walls of which secrete a great 

 deal of mucus, seems to be developed somewhat at the expense 

 of this organ. 



