GONYOSTOMUS. Vll 



vas deferens and retractor at its summit. The vagina is long, and 

 continued in a sort of pouch above the entrance of the spermatheca 

 duct (pi. 52, fig. 27). The latter is slender and nearly as long as 

 the oviduct. The ovisperm duct is imbedded in the concave side of 

 the albumen gland nearly to the distal end of the latter. 



The intestinal tract is of the usual four-folded type. The jaw is 

 strong, arcuate, solid and smooth, with a slight median projection 

 (pi. 57, fig. 59, G. turnix), or highly arched with a strong projec- 

 tion (pi. 57, fig. 67, G. multicolor). The radula has the formula 

 39.1.39 in G. tvrm'x (pi. 57, fig. 68). The central and lateral teeth 

 bearing single, broadly rounded cusps. The change to marginal 

 teeth begins about at the 15th tooth, a division of the cusp into 

 mesocone and ectocone gradually ensuing. A few extreme marginals 

 are irregular in shape, as usual. In G. multicolor (pi. 57, figs. 65, 

 66) the formula is about the same, but the cusps are longer and less 

 broadly rounded. 



Type G. goniostoma. Distribution, southern Brazil. 



This genus was formerly considered a subgenus of BulimulidcR 

 subordinate to Auris. The examination of alcoholic specimens of 

 two species, received from Dr. H. von Ihering, shows that it has no 

 affinity to Auris or other Bulimuline genera, but is a member of the 

 Strophochilince, closely related to Strophocheilus, from which it 

 differs chiefly in the form of the shell. The form of the kidney, 

 absence of any tubular ureter, the pattern of the lung, the solid jaw, 

 unicuspid, median teeth of the radula, in fact the whole anatomy, is 

 Strophocheiline, and widely different from the Bulimuloid genera. 



My former treatment of this group is an instructive commentary 

 on the inconclusive nature of purely shell characters. Before I had 

 dissected Gonyostomus I thought it a member of the Bulimulidse, 

 while Thaumastus I took to be a subgenus of Strophocheilus ; whereas 

 the anatomy conclusively shows that Gonyostomus belongs to the 

 Strophochilinse, and Thaumastus is a typical member of the Buli- 

 mulinse. And in dealing with both genera I had before me speci- 

 mens of the shells of nearly every species for study. 



The genitalia of Gonyostomus present some interesting features. 

 The vas deferens in G. tarnix adheres to the vagina, upon which it 

 pursues a sinuous course (pi. 51, f. 16). The vagina is plicate 

 within (pi. 52, fig. 27, G. multicolor, v, vagina ; sp, lower end of the 

 spermatheca duct ; o, lower end of the oviduct ; s, accessory sac). 



