1922] NATURAL SCIENCES OF PHILADELPHIA. 31 



like portion (Plate IV, fig. 17b) is continuous with a thickening 

 on the central posterior side of the tooth; this thickening runs 

 diagonally from the base to near the inner tip of the comb-lateral. 

 Outside of the handle-like portion is a thinner, triangular portion 

 portion (Plate IV, fig. 17c), which fits over the inner end of the 

 accessory plate. The anterior (upper in figures) edge of this 

 triangular portion is often thickened and reflected, so as to form 

 a continuation (Plate IV, fig. 17d) of that which bears the cusps. 

 On the under-side of the comb-lateral is a saddle-shaped de- 

 pression or hole (Plate IV, fig. 17e) dotted lines, into which fits 

 the base of the comb-lateral next anteriad. 



The accessory plate (Plate IV, fig. 17, right) is a large, but 

 usually thin and transparent, trapezoidal plate, externad to the 

 comb-lateral. The inner end (Plate IV, 17f) fits under the tri- 

 angular outer portion of the comb-lateral. In many species, all 

 of the anterior edge, except that of the outer lanceolate appendix 

 (Plate IV, 17g) is reflected to form a broad ledge (Plate IV, fig. 

 17h). This is often strengthened by thickenings of various shapes, 

 and appears to form a support for the comb-lateral. In Hender- 

 sonia and Oligyra, this reflected portion appears to form a wing, 

 which completely invests the base of the comb-lateral so as to mask 

 its inner cusps. In many other genera, it is much reduced and 

 only connects with the outer prolongation of the cusp-bearing 

 portion. In the figures where the two pieces are shown separated, 

 the position of the inner end of the accessory plate is marked by 

 an (x) on the comb-lateral, while that of the outer extremity of 

 the comb-lateral is marked on the accessory plate in the same 

 manner. 



The above description is based on the laterals of the Helicininae. 

 In the group of species that center around the genus Eutrochatella 

 (Vianinae), the capituliform complex is so highly modified as 

 hardly to be recognizable. The accessory plate is much reduced, 

 while the comb-lateral is represented by a large T-lateral. The 

 latter is very much the shape of half of a mushroom. It bears a 

 broad, reflected cusp, which is semicircular in outline as viewed 

 from the anterior end, while the stalk portion is about at its middle. 

 The accessory plate usually has a rather heavy anterior thickening 

 which may form an inner hook, and fits over the outer branch of 

 the stalk. 



In the normal position, the accessory plate and the outer portion 



