8o collinge: non-operculate land and freshwater molluscs. 



one another. Those in B are here figured and described (PI. iv, 

 fig. 1 8). The chief differences from those described in the form A are, 

 the general position of the organs, the form of the male organs, 

 free-oviduct, and the densely convoluted common duct. 



Proximally the penis is surrounded by a muscular collar, and is 

 shorter than in the form A. At the inner side of the muscular collar 

 there is inserted a small muscle (PL iv, fig. i8, 7n^), which is continuous 

 with one inserted in the end of the kalk-sac (PI. iv, fig. i8, 7ir). There 

 is a small diverticulum, the retractor muscle of the penis being inserted 

 at its distal end. The epiphallus is very short, practically a small 

 connecting duct between the penis and vas deferens. The kalk-sac 

 is smaller than in form A. The vagina is comparatively short, the 

 receptaculum seminis sessile, and usually without any muscle. 

 Externally the free-oviduct appears as a large, globose mass for the 

 greater portion of its length, internally, however, the actual cavity is 

 considerably smaller than one would at first suppose (PL iv, fig. 28, 

 f.oi\). Commencing at the external generative orifice the internal wall 

 of the vagina has quite smooth walls, but passing distally they become 

 plicated, and at the point where the sharp bend occurs at the junction 

 of vagina and free-oviduct, the walls become very richly folded, and 

 again quite smooth in the free-oviduct (PL iv, fig. 19). 



The Free AIut<rJes (PL iv, figs. 20-22). — In the form A the buccal 

 retractor forms a thick broad band, tapering posteriorly at its origin 

 and dividing anteriorly into two narrow bands, which are inserted into 

 the walls of the buccal cavity posteriorly and ventro-laterally. The 

 retractors and inferior tentaculars are on both sides fused together, 

 while more posteriorly the combined pedal and inferior tentacular join 

 the superior tentacular, passing backward as a single band (PL iv, fig. 20). 

 In the form B the buccal retractor is as in A. The pedal re- 

 tractor arises from the superior tentacular, and then posteriorly the 

 superior and inferior tentaculars unite (PL iv, fig. 21). 



In the form C the buccal retractor commences as a broad band, 

 which soon bifurcates, the two branches then being similar to those in 

 A and B. The superior and inferior tentaculars fuse much more 

 anteriorly than in either A or B, after the fusion the pedal retractor 

 arises, and some distance behind a further pedal (PL iv, fig. 22). 



The Pallial Organs (PL iv, fig. 23). — The kidney is a little more than 

 half the length of the lung, the latter measuring 102 millim., and the 

 former 62 millim. The ureter passes off from the anterior border, at 

 its commencement it is slightly more than 5 millim in breadth, but 

 posterior to the region of the pericardium it narrows forming a tube of 

 uniform dimensions. The posterior border of the pericardium is 



