94 PROCEEDINGS OF THE ACADEMY OF [Feb.^ 



9. Dinophilus pygmseus. 



Verrill, 1S92.— Scliimkewitsch, 1895.— Schultz, 1902. 



Head equal in width to first trunk segment, bearing two complete 

 ciliated bands. No circumanal band present. Caudal appendage 

 sliort and unsegmented. Male unknown. Color, (?). Length, 0.7 mm. 

 Habitat, Woods Hole, Massachusetts, U. S. A. 



Unrecognized Species. — 



Dinophilus sphceroccphalus Schmarda, 1S59. Guayaquil, S. A. 

 Description scanty and inadequate. 



Dinophilus borealis Diesing, 1862. This species is considered by 

 Diesing to be equivalent to Plagiostomum horealc 0. Schmidt, and 

 Vortex vittata Frey and Leuckart. It is probably a true turbellarian. 



Dinophilus Jensen, 1878. 



Dinophilus caudafus Levinson, 1879-80. Levinson, curiously 

 enough, considers this species identical with D. vorticoides 0. Sch., and 

 also with Planaria caudata of Fabricius {Fauna Groenlandica) and 

 Miiller {Zoologica Danica). I was unable to satisfy myself that this 

 was the case, and therefore allowed Sclimidt's name to stand. 



Dinophilus rostratus Schultz, 1902. This curious form is clearly not 

 a member of the genus Dinophilus, whatever its relationships may be. 



2. Body Wall. 



The body wall consists of the hypodermis and the circular and longi- 

 tudinal muscles. It also contains the longitudinal nerve cords, as 

 well as sensory cells; these are described in the section on the nervous 

 system. 



The hypodermis is a simple epithelium whose cells rest internally 

 upon a thin basement membrane, and are clothed externally by a 

 cuticle. The body wall, generally speaking, is quite thin relative to the 

 size of the animal, but its thickness differs much in the various parts 

 of the body, and also varies in proportion to its degree of contraction. 

 In the region of the head, more particularly on its ventral side, the 

 hypodermis reaches its greatest thickness, about 15 pt. In the trunk 

 there is a thickened portion along the ventral side,^ roughly coincident 

 with the ciliated area of this region; it is slightly thicker near the 

 middle of its length than at the ends (figs. 6, 7, 8 and 9), In the 



^Shearer (1906) has compared this thickened area with the "crawling pad" 

 of the TurbeUaria. It is, however, rather to be compared to the ventral plate of 

 annelid larvte, since it is formed in the same manner and from the same cleavage 

 cells (Schimkewitsch, 1895; Nelson, 1904). 



