330 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 45. 



Figure 7 shows a mold of the interior of a pedicle valve (magnified 2 

 diameters) . It exhibits the characteristic ridges bounding the muscu- 

 lar scars which may be compared with the corresponding views of 

 pedicle valves of LeptostropMa Jilosa illustrated by figures 1 and 2> 

 which are natural size, and 9a, which is magnified 2 diameters. 



LeptostropMa Jilosa which occurs in the same beds with this species 

 is flatter, though Brachyprion shaleri is also nearly flat. 



Formation arid locality. — Edmunds formation from the outcrops on 

 the east shore of Burnt Cove, south of Cunningham Mountain (loc. 

 No. 5.51. 5B), and west of Field Pomt, southeast of Ball's Mountain 

 (loc. No. 8.1.8A), and west shore of Cobscook River, opposite Wilbur 

 Point (loc. No. 8.21. lA), all in Edmunds Township, Washington 

 County, Maine. 



Coty pes. —Csit. Nos. 58950, 58951, 58952, U.S.N.M. 



ON THE GROUP OF AVICULOID SHELLS CALLED AVICULA? DANBYI 



BY M'COY. 



Frederick M'Coy published in the Annals and Magazine of Natural 

 History m 1851 the description of some aviculoid shells found abun- 

 dantly in the greenish quartzite (Upper Ludlow rock) of Benson 

 Knob, Kendall, Westmoreland, under the name Aviculaf danbiji 

 (M'Coy) .^ With this original description no figures were pubhshed. 

 Later in British Silurian Rocks and Fossils,^ 1855, the species was 

 redescribed and five figures were pubhshed. In both places doubt 

 was expressed as to the reference of the species to the genus Avicula. 

 The discovery in the Edmunds formation of the Eastport quadrangle, 

 Maine, of specimens evidently belonging to this group of forms has 

 led to a critical study of them and of M'Coy's descriptions and figures 

 with the result of discriminating certain distinct generic characters 

 for the group, resolving the forms described by M'Coy into two dis- 

 tinct species and the recognition of a new species among the Maine 

 representatives of the genus. 



M'Coy, in writing his description, evidently had before him speci- 

 mens of each of the three specific forms, recognizing the wide range 

 of variabifity and writing his description to cover the middle species- 

 This is indicated by his giving "average" dimensions, by the state- 

 ment that the species ''varies much in the amount of its obliquity 

 and transverse elongation and the number of radiations on the left 

 valve," also ''some of the varieties are so slightly obhque as to 

 assume a rotundate-quadrate form." 



In resolving the group into its constituent species I have taken the 

 form represented by figure 13 of his plate IZ. as most closely conform- 

 ing to his definition of the species Aviculaf danhyi. The figures 11 

 and 15 represent a smaU and a large specimen of the same species. 



1 Silurian Mollusca, Ann. Nat. Hist., ser. 2, vol. 8, 1851, p. 59. 

 » Idem, p. 258, pi. II., figs. 11-15. 



