342 PR0CEEDIXG8 OF THE NATIONAL MUSEUM. vol.45. 



indicated by the figures given by Davidson.^ Our specimens from 

 tlie Pembroke formation present similar variation in form, but 

 throughout the formation are distinguished by their small size. 

 They undoubtedly represent the Lingula minima Sowerby, and the 

 application of a variety name to them {L. minima var. americana) is 

 suggested by the difficult}' experienced in determining which of the 

 various forms expressed by Davidson's figures may be regarded as the 

 type of the species. 



PELECYPODA. 



Genus ACTINOPTERIA Hall. 



ACXmOPTERLA. BELLA, new species. 

 Plate 30, figs. 17, 19. 



Shell oblique, ovate; both valves convex; left valve the larger; 

 posterior wing accuminate; anterior ear small, triangular; both wing 

 and ear strongly defined from the central body part of the shell j 

 beak of the left valve strong, rathei; broad, overarching the cardinal 

 border, body of the shell convex, flattened over the center. Beak of 

 right valve smaller than the left and scarcely reaching beyond the 

 cardinal border; right valve gently convex, sloping gradually into the 

 posterior wing; body portion separated from the anterior ear by a 

 shallow furrow. Surface of the left valve over the body part crossed 

 by rounded distinct radiating lines, which are absent from the ear 

 and wing; crossed by finer concentric lines over the whole surface. 

 The whole surface of the right valve crossed by fine concentric lines, 

 without distinct radiatmg lines; upon some specimens very faint 

 radii are visible over the body portion. In some large specimens 

 referred to the species the radiating lines become obsolete upon the 

 extreme border of the left valve, forming a rim of 2 or 3 mm. wide 

 crossed only by concentric lines. 



Dimensions of type-specimen (Xo. M1216.1, pi. 30, fig. 17, a left 

 valve) from tip of anterior ear to posterior-ventral angle, 22 mm.; 

 hinge, IS mm.; hinge to vent margin, 14 mm. Corresponding meas- 

 urements of cotype of right valve (specimen No. M1217, pi. 30, 

 fig. 19), 19, 20, and 13 mm. Smaller specimens than the t}^es show 

 the beak of the left valve narrower and more gibbous, but in full- 

 sized specimens the central body portion becomes broadly convex. 



Formation and locality. — Shales of Pembroke formation at the head 

 of Leighton Cove, at the southern end of Pembroke Township, Wash- 

 ington County, Maine Goc. Xo. 5.3.8M0- 



Coty pes. —isit. Xo. 5S964, U.S.X^'.M. 



1 Brit. Sa. Brach., pi. 2, figs. 36-44. 



