206 PLATHELMINTHES 



circular, an inner longitudinal, to which a third, an inner circular, is 

 sometimes added; lateral nerves either external to the muscles or 

 imbedded in the longitudinal layer; cutis absent: 4 families, all marine. 

 Key to the families of Paleonemertea here described: 



Oj Paired intestinal diverticula absent 1. CABINELLIDAE 



o 2 Paired intestinal diverticula present 2. CEPHALOTBICHIDAE 



FAMILY 1. CABINELLIDAE. 



Cerebral organs represented by a pair of lateral epithelial depres- 

 sions; brain and lateral nerves lie in the outer epithelium or just 

 beneath it ; mid-dorsal blood vessel usually absent ; inner circular muscles 

 encircling the proboscis sheath and intestine very thick: 5 genera and 

 about 27 species. 



CARINELLA Johnston. Body cylindrical and filiform, with the head 

 end large and distinctly set off; intestinal diverticula absent; lateral 

 sense organs usually present near the paired excretory pores, consisting 

 each of a round ciliated depression : 16 species, principally on the Pacific 

 coast. 



C. pellucida* Coe. Body very small, whitish in color, up to 25 mm. 

 long and .5 mm. thick: not uncommon among annelid tubes at low water 

 and below in Long Island and Vineyard Sounds; California. 



FAMILY 2. CEPHALOTRICHIDAE. 



Body long and very slender, usually filiform; cerebral organ and 

 eyes usually absent; mouth behind the brain; body wall contains two 

 muscle layers, an outer circular and an inner longitudinal, with the brain 

 and longitudinal nerves lying in the latter layer: 2 

 genera and about 12 species. 



1. CEPHALOTHRIX Oersted. Body filiform, taper- 

 ing at the forward end, which is pointed; no excre- 

 tory canals; inner circular muscles absent; the worm 

 coils the body in a spiral: about 7 species. 

 IB C. linearis (Rathke) (Fig. 334). Body whitish, 

 yellowish, or flesh color, up to 15 cm. long and 1 mm. 

 thick; mouth very far back; proboscis very long and 

 slender: Long Island Sound to Nova Scotia; Pacific 

 coast; Europe; often common between tide lines, under stones and in 

 the sand; breeds in August at Woods Hole. 



2. CARINOMA Oudemans. Body rather thick, cylindrical in front, 

 flattened behind: 4 species. 



* See "Descriptions of Three New Species of New England Paleonemerteans," 

 by W. R. Coe, Trans. Conn. Acad., Vol. 9, p. 515, 1895. 



