TRACHYDERMON. 



T. QOTHICUS Cpr. PI. 15, figs. 28, 29. 



The original description will be found on p. 74, vol. xiv. 



The type of this little shell was collected at Catalina Island by 

 Cooper. It is an exceptionally elevated species, the dorsal ridge 

 being acute, and the angle of divergence about 80. The type (Mus. 

 Smiths. Inst. 16271) having been glued to a glass tablet formerly, 

 is not in very good condition, but Carpenter's excellent description 

 and the figures here given (representing the half of a median valve 

 and a profile of the tail valve), will readily identify it. 



T. RUBER L. PI. 15, fig. 25 (girdle-scales, x 125). 



T. DENTIENS Old. PI. 15, fig. 26 (girdle scales, x 250.) 



Subgenus SPONGIORADSIA Pilsbry, 1894 (n. s.-g.) 



Trachyradsia CPR. in part, exclusive of its type Ch. fulgetrum. 



Valves smoothish, having two or several side slits, and extremely 

 spongy eaves and sinus, the latter squared. Girdle sparsely beset with 

 minute elongated scales. Type Tr. aleutica. 



It is somewhat doubtful whether this group should rank under 

 Callochiton or Trachydermon ; but as the girdle, sinus and gills more 

 resemble the latter, I have placed it here. The spongy eaves and 

 radsioid valves resemble Trachyradsia (plus Stereochiton), but the 

 sinus in that group, as in typical Callochiton, is bridged by a lamina 

 extending across from one sutural lamina to the other. 



But two species are known to belong here : aleutica Dall and multi- 

 dentata Cpr. 



T. ALEUTICA Dall. PL 15, figs. 30, 31, 32, 33. 



The original description is given on p. 84, vol. xiv. 



This is a small, dull purplish-red species, much elevated but 

 rounded at the ridge, valves broadly v-shaped, the anterior border 

 of each being concave, the lateral areas a trifle raised but 

 indistinct, whole surface obsoletely punctulated by the comparatively 

 large megal aesthetes, and showing some lines of growth. 



The most prominent characters are presented by the interior of 

 the valves, which are flesh-colored, rather thick, and have the pos- 

 terior border of the tegmentum broadly reflexed. The wide eaves 

 are coarsely and densely spongy, the teeth being reduced to very 

 slight prominences or wholly obsolete on some valves ; but the num- 

 ber of punctate slit-rays shows that the side-slits if developed would 

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