PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 387 



Polycerella Emertoni Verrill, sp. nov. 



Body small, elongated-ovate, rather narrow, somewhat angular, about 

 as high as broad, sometimes higher than broad, tapered and somewhat 

 acute posteriorly, narrowed a little at the neck. Head high, convex 

 above, sometimes bilobed, but often rounded in front, capable of chang- 

 ing its form to a great extent, the part in front of the dorsal tentacles 

 being capable of considerable elongation and of contracting to a truncate 

 form. Foot high and narrow, obtuse posteriorly, the anterior angles 

 l>rolouged into short but prominent auricles, often curved backward and 

 pointed, at other times short and blunt. Dorsal tentacles rather long, 

 not retractile, but capable of considerable contraction ; in extension 

 their length is often equal to the breadth of the neck; they are fusiform 

 or subclavate, blunt, smooth or shoeing only slight, transverse, irregular 

 wrinkles, changeable in form, sometimes nearly cylindrical, at other times 

 swollen in the middle or toward the tip. Edge of the mantle indicated 

 only by a slight, often crenulated, ridge along each side and around the 

 head. Above this edge there is a row of small papilla?, of which two on 

 each side are in advance of the dorsal tentacles ; two are opposite to 

 them, and four or five on each side occupy the space between the tenta- 

 cles aud gills ; a row of five or six, on each side, extends l)eyond the gills 

 to near the end of the body, the posterior ones becoming verj' small. 

 Behind the gills there are three or four pairs of larger and longer -pn- 

 pillaj, situated more dorsally; of these the two pairs next to the gills 

 are longest, and are often nearly equal to the dorsal tentacles in size 

 and length ; they are usually somewhat swollen in the middle and blunt 

 at the tip. Two or three pairs of much smaller papillre are situated on 

 the back, in front of the gills. Gills three, narrow, elongated, pinnate, 

 subplumose, not finely divided, curved backward, not retractile, about 

 equal in length to the dorsal tentacles; the pinntie are few, alternate, 

 generally incurved, those toward the base more slender. 



Color yellowish green to olive-green, varied with lemon-yellow, and 

 blotched and sjjccked with darker green or blackish ; foot, tentacles, 

 gills, and dorsal papilhe lighter greenish yellow, sparingly specked with 

 dark green. 



Length, o-""' to 6™"; breadth, l"-"; height, 1.12""°; length of rhino- 

 phores, .88'"'". 



The odontophore is very minute. The teeth of the inner row, on each 

 side, are relatively very large and long, stout, with the shaft bent back- 

 ward and the end abruptly curved forward and divided into two sharj) 

 denticles ; another sharp denticle is situated laterally, below the others. 

 The two outer lateral rows of teeth are much smaller and less than half 

 the length of the inner ones, nearly equal in size aud form, simple, 

 strongly curved forward, and very acute. 



This species was first taken by the writer at AVood's Holl in September, 

 1875, at the surface, among eel-grass; and on hydroids from the piles 

 of Long Wharf, New Haven, Conn., October, 1875. At Newport, 11. 1., 

 it has been fouud several times by Mr. J. H. Emerton and the writer, iu 



