58 The Molluscan Family Plauorhidae 



Internally the penial complex has certain distinctive features, as shown 

 in fig. 10 on plate 6 ispirorbis) . The preputium has two vertical ridges or 

 pilasters. Between the preputium and the vergic sac there is a thick 

 muscular ring which shows as a swelling on the exterior surface of the 

 upper part of the preputium. A large papilla (PP) is suspended between 

 the walls of the muscular ring, the walls of which are very thick. 



Below the large muscular swelling there is a second smaller ring which 

 is here called the diaphragm (D). It is relatively thin and is capable of 

 considerable contraction and expansion, which causes the hole or foramen 

 in the middle, as viewed from above, to be small or large. Buchner shows 

 this ring (Ringwulst) in his fig. 1 on plate 5, but it is there shown in 

 section as almost closed and is placed below the thick papilla. In those 

 specimens of the four species examined the ring has been widely open and 

 the papilla has been extended below the area of the ring (plate 6, fig. 4, 

 vortex, fig. 10, spirorbis) . The papilla is larger and somewhat differently 

 shaped in the figures on plate 6, varying in this respect from Buchner's 

 figure. Possibly changes due to breeding condition may be the reason for 

 this difference. 



The verge is long, cylindrically pyriform in shape above and tapering 

 rapidly below the middle of its length to form a slender tube, at the end 

 of which is a small, horny stylet. The sperm canal turns to the side just 

 above the stylet where it has its exit on the side of the verge (plate 6, figs. 

 4, 5). The stylet is sharp and needle-like, bulbous at the upper part where 

 it is attached to the verge. There is a fine groove extending along one 

 face of the stylet (plate 6, figs. 2, 5; plate 7, fig. 5). The verge of vortex 

 is much narrower than that of any other species examined. With the excep- 

 tion of the 'Ringwulst' the penial complex of the four species of the genus 

 Anisus agrees with the description and figure of Buchner. 



Female Organs. The spermatheca is much elongated and cylindrical 

 in vortex, spirorbis, and septemgijrntus with a spermathecal duct about as 

 long as the spermatheca (plate 6, fig. 12). In leucostomus, however, the 

 spermatheca is short and bulbous with a short, thick spermathecal duct 

 (plate 7, fig. 2). In several specimens of septemgyratus the spermatheca 

 was cylindrical and acutely pointed at the summit. One specimen contained 

 a large spermatophore (plate 7, fig. 6). The spermatheca and its duct are 

 over 1 mm. long in spirorbis, but less than a millimeter in leucostomus. 



The vagina (V) is very short (less than 0.3 mm.) in all species. The 

 uterus (U) is long and cylindrical in vortex, septemgyratus, and spirorbis, 

 but rather short and wide in leucostomus. The nidamental gland is long 

 and cylindrical in vortex, spirorbis, and septemgyratus but large and swol- 

 len in leucostomus. The oviduct shows the same differences, being long and 

 cylindrical in vortex, spirorbis (3 mm. long), and septemgyratus, but is 

 short (about 2 mm. long) and of larger diameter in leucostomus. The ovi- 

 duct is always of greater diameter than the sperm duct (see figs. 2 and 

 6, plate 7, fig. 12, plate 6). The albumen gland is elongated, narrow, and 

 somewhat arched (plate 6, fig. 9; plate 7, figs. 2, 6, AL). 



Hermaphrodite Organs. The ovotestis is made up of many club-shaped 

 diverticula arranged in a double row on the ovisperm duct (i)late 6, fig. 

 12; plate 7, fig. 2, OT, spirorbis and leucostomus). Two diverticula of 

 leucostomus are shown on plate 6, fig. 7. Several diverticula of vortex had 

 ripe ova. The ovisperm duct is divided into two parts separated by the 



