BRACHIOPODA. 309 



teeth are moderately developed, and indicate considerable divergence in the 

 dental ridges. A most remarkable feature on these casts, is the presence, on 

 each side of the umbo, of a minute, greatly elongate and gently tapering cone, 

 the base of which is joined to the cast at about two-thirds the distance from 

 the apex to the cardinal angle; and from this point each one is inclined toward 

 the apex of the shell, and terminates in a free extremity. These delicate 

 cones which are so fragile that they are easily lost and rarely preserved, 

 penetrate, but do not transect the cavity originally filled by tlie substance of 

 the cardinal portion of the valves ; they are evidently the casts of a single pair 

 of large and very oblique spine-tubes, which were not continued into spines as 

 in Chonetes, and evidently did not penetrate to the outer surface of the cardi- 

 nal margin. The inner opening of these blind tubes is situated below and in front 

 of the cardinal area, and their obliquity greatly exceeds that observed in the cardi- 

 nal tubes of Chonetes. The muscular impressions consist of two tlabellate diduc- 

 tors, between which lie two elongate, narrow adductors. Over the pallial region 

 the surface is pustulose. In the brachial valve the cardinal process appears to 

 be simply bilobate, the crural plates narrow and obscure. From the base of the 

 cardinal process extend two slightly divergent median ridges which are con- 

 siderably elevated at the center of the shell and terminate abruptly. These 

 enclose an elongate muscular scar. There are also two lateral ridges curving 

 outward and then inward, enclosing small thickened areas which appear to be 

 of muscular origin, while the ridges themselves have the curvature of, and 

 suggest the " reniform impressions." Nearly the entire inner surface of this 

 valve is covered with radiating rows of strong pustules. This curious shell 

 represents a phase of development in the chonetid type not hitherto described 

 and it may be convenient to separate it under the sub-generic name Anoplia.* 

 Illustrations of the only species known to possess these features, Leptczna ? 

 nucleata, will be found on Plate XV a, figures 17 and 18, and Plate XX, figures 

 14-17. 



*Mebk and Worthen, in describing' this species under the niinie Leptmna'^ midiata (Palaeontology of 

 Illinois, vol. iii, p. 394 ; 1868), observed that '• this curious little shell does not pi-esent the form or internal 

 cliai-acters of Lbpt^na, and will i)robably be; (bund to be a new genei'ic type." 



