170 



COB 



The head is continuous with body and provided with four ocelli. 

 Proboscis armature as in other species of Tetrastemma. 



Habitat. — On piles of wharves, on rocks, among alg£e, bryozoa, 

 ascidians and other growths. Widely distributed in Northern Hemi- 

 sphere, occurring on the northern coasts of Europe, in the Mediter- 

 ranean and on both the east and west coasts of North America. 



14. TETRASTEMMA (CERSTEDIA) RETICULATUM 



sp. nov. 



p1. xrv, figs. 7, 8 ; pi. xx, fig. 7-9. 



A minute species measuring but 8-15 mm. in length when sexually 

 mature, and less than 0.5 mm. in diameter. Body short, thick, 

 rounded ; much resembling Oerstedia in form and movements, as 

 well as in firmness of body and in general appearance. The peculi- 

 arities of the species are not sufficiently pronounced, 

 however, to warrant its separation from the genus 

 Tetrastemma . Head usually somewhat narrower 

 than body, from which it is usually distinctly 

 marked off by a pair of oblique lateral grooves. 

 These lie opposite the posterior pair of ocelli (pi. 

 XIV, fig. 8), as in related species. 



Color. — General color of body white, with rec- 

 tangular and longitudinal brown markings which 

 obscure most of the white color of dorsal surface. 

 Two varieties, presenting widely different arrange- 

 ment of the dorsal markings, were met with, and 

 these in extreme cases would suggest two different 

 species. In both varieties the head, which is white 

 or colorless, is provided with a very similar trans- 

 verse deep brown marking between the anterior and 

 posterior pairs of ocelli. This marking consists of 

 a transverse band of color extending laterally some- 

 w^hat beyond the ocelli, and having a rounded and 

 deeply bilobed anterior margin (text fig. 21). It 

 is often shaped like a dumb-bell, except that the 

 contour is straight, and not indented, posteriorly. 

 In the 'most common variety (p1. xiv, fig. 7) there are about sixteen 

 pairs of rectangular brown markings situated on the dorsal surface and 

 extending from the head to the posterior end of the body. These oc- 

 cupy the greater portion of the dorsal surface, leaving but little space 



Fig. 21. T. retic- 

 ulatum. Outline of 

 anterior portion of 

 body, showing posi- 

 tion of ocelli and 

 shape and arrange- 

 ment of markings. 

 X40. 



