484 MOLLUSCA 



body covered with spieules, also with papillae; no radula present, the 

 pharynx being protrusile: 1 genus; North Atlantic, Mediterranean Sea, 

 and West Indies. 



NEOMENIA Tullberg. With the characters of the family: about 

 4 species. 



N. carinata Tull. (Fig. 743). Body 2 to 3 cm. long 

 and half as thick ; back with a keel : North Atlantic. 



Fig. 743 Neo- FAMILY 2. PEONEOMENIIDAE. 



menia carinata 

 (Cambridge Nat- Body elongate, 9 to 14 times as long as thick ; radula 



ui'til History). 



present; body covered with spieules: 4 genera. 

 PRONEOMENIA Hubrecht. With the characters of the family: 2 

 species. 



P. sluiteri Hub. Length 10 to 14 cm. : Arctic seas. 



SUBORDER 2. CH^ETODERMATINA. 



Mouth and cloaca terminal; head end and hinder end set off by con- 

 strictions; body cylindrical, without ventral groove, and covered with 

 spieules; 2 feathered gills present; sexes separate: in the North Atlantic 

 and the Pacific Oceans, burrowing in the mud; 2 genera. 



CiLffiTODERMA Loven. With the characters of the suborder: 3 

 species. 



C. nitidulum Lov. (Fig. 744). Length 25 mm.; width 2 mm.: coast 

 of Scandinavia and northern America; Gulf of Maine; in 100 fathoms. 



ORDER 2. POLYPLACOPHORA.* (CHITONS.) 



Body from 10 mm. to 15 cm. in length, elliptical in shape, convex 

 dorsally and flattened ventrally, and bearing on its dorsal surface a lon- 

 gitudinal row of eight calcareous plates or valves (Fig. 745). These 

 plates possess characteristic form and markings and usually overlap pos- 

 teriorly. They are composed of two distinct layers, the lower layer, 

 the anterior portion of which extends forwards beneath the overlapping 

 valve in front of it and is called the articulamentum, and the exposed 

 layer, which is the tegmentum. They are surrounded and kept in place 

 by a muscular integumental fold called the girdle, the portions concealed 

 by the girdle being called the insertion plates. In Cryptochiton the 

 girdle entirely covers the shell, and in several other genera it almost covers 



* See "On Certain Limpets and Chitons from the Deep Waters of the Eastern 

 Coast of the United States," by W. H. Dall, Proc. U. S. Nat. Mus., Vol. 4, p. 400. 

 "Polyplacophora," by H. A. Pilsbry, Man. of Conch., Vol. 14 and 15, 1892. "Chitons 

 Collected by Dr. Harold Heath," etc., by H. A. Pilsbry, Proc. Acad. Nat. Sci., 

 1898, p. 287. 



