NO. 2225. NUCULITE8 FROM THE MAINE SILURIAN— WILLIAMS. 45 



falls off toward the base in a nearly straio;ht line to the middle, then 

 gently curves around the postero-basal angle into the basal margin. 

 The front margin is gently arched, running into the basal margin in a 

 broad regular curved line. The anterior side is shorter than the pos- 

 terior and their margins are subparallel. The hinge is arched and 

 shorter than the transverse diameter of the shell. The clavicle is 

 slender and short, extending about one-third distance to the base. 

 The hinge is crenulate. The surface is marked by fine concentric 

 lines; and, in this specimen, is marked by several small pustulous 

 elevations, which are seen to be produced by Ostracods lying inside 

 the shell and pressed into the shell during fossilization, thus showing 

 the thin structure of the shell. 



Another specimen from the same locality is M 1790 A (pi. 11, fig. 3). 



Dimensions of 1791: length 15 mm. ; height 17 mm. (113 per cent). 



No. 1790, transverse diameter, 14, estimated height 19 mm. (135 

 per cent). 



The type-specimen shows faint indication of an umbonal furrow, 

 and in the umbonal region it is bounded by a slight indication of an 

 imibonal ridge. 



The second specimen shows some faint indication of wrinkling of 

 the surface in the direction of the long axis of deformation of the 

 shales in which it lies. 



Both specimens lie with the transverse axis of the shell, at near 

 right angles to the axis of elongation of the shales, thus clearly indi- 

 cating the metamorphic nature of their specific characters. 



Formation and locality. — Pembroke f onnation, gray, splintery shales, 

 Kelley Point, south shore of Pannamaquam River Qoc. No. 5.3,2 A). 



Type-specimen.— Cat. No. 62889, U.S.N.M. 



NUCULITES EURYLOCHUS, new species. 



Plate 11, fig. 4. 



Shell of medium size, subcircular, length and height about equal, 

 margins regularly rounded. Valves moderately convex below, 

 becoming gibbous a little above middle. Beaks a little anterior to 

 the middle, small, rising but little above hinge line. Posterior slope a 

 little longer than the anterior slope and marked by a curved dejires- 

 sion fading out toward the hinge and toward the base. The clavicle 

 distinct, erect and distinctly in front of the beak, reaching nearly half 

 way across the shell. Test thin. Surface marked by fine concen- 

 tric strias and at irregular distances stronger growth lines. The crenu- 

 lations of the hinge are not actually seen, but their presence is inferred 

 from the fact that the specimens of N. galeus on the same slab (1790 A) 

 show the crenulations and the two agree in other characters of the 

 shell except form. 



This species, like N. galeus, is regarded as a metamorphic species 

 (namely, the acquired are more prominent than the original char- 



