Fam. 70] NATURAL HISTORY SOCIETY. 149 



ridges on the body whorl, with numerous very fine lines; these, 

 with the rather coarse lines of growth, give the surface an in- 

 dented or cellular appearance ; apertur# circular ; umbilicus 

 large and deep, bounded by a sharp, angular ridge. Dull red- 

 dish-brown above, and light ash-color below. L. 10; D. 12; 

 An. 90°; Wh. 5; Ap. f.— New England. Found in fishes. 

 Order POLYTLACOPHORA. (The Chitons). 

 Body vermiform; symmetrical, without separated head or 

 tentacles ; ventral surface flattened ; dorsal surface covered by 

 calcareous plates, placed in a segmented manner, one behind the 

 other ; gills paired. 



Family 70. ISCHNOCHITONID/E. 

 Animal furnished with eight, calcareous plates along the back ; 

 the head and tail piece similarly articulated ; the insertion plates 

 sharp, smooth, fissured ; the outer layer around the plates called 

 the girdle overhanging the plates and forming eaves. 



* Eaves projecting- ; girdle covered with minute flattish scales 



: 1. Trachydermon. 



* Eaves moderate ; girdle covered with hairs 2, Chcetopleura. 



^ Eaves short ; girdle minutely downy '. 3. Tonieella . 



Trachydermon, Carpenter. 

 Anterior and posterior plates with many sharp teeth ; girdle 

 covered with minute granular flatfish scales, and without pores; 

 eaves projecting, spongy ; gills short. 



1. Trachydermon ruber^ Low. Shell small oval, elevated, 

 keeled ; lines of growth distinct, but surface unmarked with 

 punctures or granulations, even under the magnifier ; color light 

 brick-red or flesh-color; margin coated with red and white dust 

 in alternate blotches; interior bright rose-red. L. 12; W. 7^. — 

 New England. On stones below low water. 



2. Trachydermon albus, Mont. Shell small, elongated-oval, 

 covered with bluish-black pigment which easily rubs ofi", and 

 leaves the color yellowish or ashy; valves moderately keeled, 

 and minutely beaked ; margin membranous, and covered with 

 beaded granules. L. 10; W. 4. — Cape Cod and north. 



2. Ch^topleura, Shut. 

 Anterior and posterior plates with many sharp teeth ; surface 

 of girdle hairy ; eaves moderate ; gills encircling. 



