428 A. E. Verrill — Marine Nemerteans of Neio England, etc. 



Some of the flat species included in this genus by Mcintosh, I 

 should, therefore, transfer to Cerebratidxis, especially his M. fnsca 

 (uoft Fabr. sp.) 



Ilubrecht has united 3ficricra and Cerebratulus without regard to 

 the form of the body and the muscidar structure of the body-walls, 

 which seem to me important characters, involving wide differences 

 in habits. 



The species of Micrura are fossorial in their habits and do not 

 swim at the surface, so far as I have observed, and, indeed, the form 

 and structure of the' body are not ada[)ted for swimming. 



Some of the species of 3Ucrura, if not all, have a Pilidium-stage 

 in development. The embryology of many of the species has, how- 

 ever, not been traced. Nor have any of the several species of Pili- 

 dium-larvse found on our coast been reared till the adidt characters 

 could be determined. On Plate xxxix, I have hgured two distinct 

 kinds of these larvae that are common at Wood's Holl, Mass., in sum- 

 mer. One or both probably belong to some of our species of Micrura, 

 but as the larval form of Gerehratidus is unknown, one of them may 

 belong to that common genus. The young nemertean seen in the 

 interior of one S])ecies (fig. 5, w), has already two distinct ocelli, 

 which would indicate that it belongs to a species like M. affinis, 

 which lias ocelli when adult. 



Micrura affinis Voniii. 



Poseidon qffiuif; Girard in Stiiiip., Marine Invert, of Grand Manan, p. 28, 1853. 

 Neinertes aj§inifi Verrill, Auier. Journ. Sci., vol. vii, pp. 39, 412, 1874; Proc. Am. 



Assoc, for ISIS, pp. 351, 363. 

 Micrura affinis Y ern\\ Proc. U. S. Nat. Mus , vol. ii, p. 18G, 1879; Check List, 



Invert., p. 12, 1879. 



PLATE XXXVI, FIOURE 1 ; I'LATK XXXVII, FIUUKES 6, 6a. 



Body elongated in extension, somewhat depressed, but with round- 

 ed sides, of nearly uniform breadth through most of the length, but 

 somewhat tapered posteriorly, and terminated by a slender, pointed, 

 pale anal papilla or cirrus, about one-half as long as the diameter of 

 the body. Head scarcely wider than the neck, elongated, flattened, 

 usually obtusely rounded anteriorly, but changeable. Lateral olfac- 

 tory slits long and deep, with thin white margins in front, uniting 

 with the proboscis-pore. Mouth of moderate size situated opposite 

 the ends of the slits. Ocelli rather large, black, conspicuous, vari- 

 able in number, forming a single row, usually of four to six on each 

 side at the edges of the white marginal areas ; the front ocelli are 



