NO. 1985. NEW SPECIES OF SILURIAN FOSSILS— WILLIAMS. 333 



SO as to express the average or middle species and in preparing his 

 plates represented this typical form by the figures numbered 11, 13, 

 and 15. I assume that figure 13 best represents the average char- 

 acters of liis species Avicula danhyi. The specific characters which 

 apply strictly to this figure are found in his definition in the terms, 

 ''oblique ovate, posterior end more or less narrowed, rounded," 

 "hinge line rather less than half the width of the shell," " both wings 

 nearly rectangular, with sharply concave margins. Average length, 

 1 inch 5 fines; width, 2 inches 3 lines; length of liinge, line 1 inch." 



Assuming these to be characters of the species Avicula danhyi in 

 strict sense, it is evident that figure 14 represents a more transversely 

 elongate form of which the anterior ear is distinctly rounded and its 

 margin undifferentiated from the general anterior convex margin of 

 the shell. The other extreme is represented b}^ Palxoyecten cobscookij 

 already described, which is suborbicular with height and transverse 

 diameter almost exactly equal. 



I have represented on Plate IV (of the Eastport Folio) each of 

 these three types, as they appear in the Edmunds formation in 

 Maine. Figures 6 and 7 are molds of the exterior of a small and a 

 large specimen of the left valve which I identify with M'Coy's 

 species as restricted. 



PAL^aSOPECTEN TRANSVERSALIS, new species. 

 Plate 29, figs. 17 and 18. 

 Cf. Avicula danhyi M'Coy (part), Brit. Pal. Foss., pi. IZ, fig. 14. 



Shell obhquely ovate, transversely elongate, greatest width nearly 

 twice the height; front margin broadly rounded, meeting the hinge 

 line at an obtuse angle without incurve or byssal sinus. Posterior 

 whig flattened, small, terminating in acute angle; lower half of body 

 much produced backward beyond the end of wing. Left valve gently 

 convex, right valve flat transversely gently concave from beak to 

 lower margin. Left valve crossed by 12 to 14 obtuse radiating 

 ridges, well defined over main body but becoming faint toward the 

 margin. Surface of both valves marked by fine, thread-like con- 

 centric lines, and irregular concentric folds which are generally 

 more marked toward the margin. Crural ridges present, one each 

 side the beak, diverging at angle of about 150°. 



Dimensions of type-specimen (No. M1407.2): Height, 33 mm.; 

 transverse width, 67 mm. ; hinge length, 40 mm. 



Formation and locality. — Same as Palxopecten cohscooM. 



Holotype.— Cat. No. 58954, U.S.N.M. 



Ohservation. — This species is distinguished from Palseopecten danhyi 

 (M'Coy) sensu stricto, by its more transverse form, the rounding of 

 the anterior ear, and the absence of incurve of the anterior margin. 



M'Coy's figure 14 of plate IZ, Brit. Pal. Foss., appears to belong to 

 this species. 



