208 A . K Verrill — Molluaea of the New England Coast. 



Station 1124, N, lat. 40° 01', \V. long. 68'' 54', in G40 fathoms, oft' 

 Nantucket Island, 1882; station 2067, N. lat. 42° 15' 25", W. long. 

 65° 48' 40", in 122 fathoms, 1888. 



Trachydermon exaratus (G. o. Sars). 



Lophyrus exaratus G. 0. Sars, Moll. Reg. Arct. Norvegiae, p. 113, pi. 8, figs. 1, a-k, 



pi, II, fig. 1 (dentition.) 

 Trachydermon exaratus Verrill, Airier. Journ. Sci., vol. xxiv, p. 365, Nov., 1882. 



Plate XXX, figures 2, 2a, 26. 



Elongated, oblong-elliptical, strongly convex ; valves distinctly 

 obtusely carinated medially. Anterior valve nearly semi-circular in 

 front; the posterior edge forming an obtuse reentrant angle, with a 

 rounded notch in the middle; surface distinctly radially grooved 

 with single rows of rounded granules between the grooves, becoming- 

 larger toward the margin. 



Median valves are moderately wide, nearly straight posteriorly, 

 the hinder ones with a slight median beak with distinct diagonal 

 fuiTows and ridges, dividing them into median and lateral areas ; the 

 median areas are covered, on the sides, with fine but very distinct 

 longitudinal grooves, with the intervening ridges narrow and 

 rounded, more or less confluent and broken up into granules, near the 

 diagonal lines, toward the median ridge becoming finer and irreg- 

 ular, and finely granulous anteriorly and along the carina. The 

 lateral areas ai*e more elevated and covered with stronger radiatingf 

 ridges, broken up into oblong and rounded, flattened granules, and 

 separated by narrow radial furrows. The lateral insertion-plates of 

 the median valves project but little beyond the upper lamina; they 

 are subtruncate, with a thin notch or slit corresponding to the diag- 

 onal line above. The posterior valve is transversely elliptical, with 

 the posterior edge evenly rounded ; the front area as in the preced- 

 ing ones ; the posterior area is covered with fine radial and 

 concentric grooves, dividing it into radiating I'ows of small rounded 

 granules ; the articulating plates of its front edge are rather wide, 

 broadly rounded or subtruncate, and separated by a broad, rounded 

 median sinus; posteriorly the inner sui face is marked by about six- 

 teen radiating lines, terminating in thin notches of the inserted edge, 

 which is very narrow and simj)le. 



The marginal membrane is rather nan-ow and covered with 

 rather stout, prominent, oblong and obtuse spinules, regularly 

 arranged in quincunx, their ends looking like granules ; at the edge 

 and on the lower side these are replaced by small, slender spinules. 



