NO. 1985. NEW SPECIES OF SILURIAN FOSSILS— WILLIAMS. 339 



ters are typically represented by the specimens on slab containing 

 figured-specimen M1204. 



Small shells from the same beds are like the corresponding part of 

 the larger shells showing only smooth plications, thus representing 

 the characters to which the names Terehratula nucula and T. pulchra 

 were given by Sowerby. 



In form the species presents the characters of Rhynchonella lewisi 

 Davidson ^ except that the fold of the brachial valve is less elevated 

 and "pinched," and the sinus shallower and broader than in the ex- 

 treme form expressed by Davidson's fig. 25, in this particular assum- 

 ing the form presented by his figure 26. In surface markings it 

 differs from Davidson's species in that the "scalelike concentric 

 ridges" do not cover the whole surface but begin rather abruptly 

 about haKway from the beak to the front margin. 



The number of plications is generally 20 and may be 22, but none 

 have been seen with 26 plications. There are three depressed in the 

 sinus and four elevated on the fold in all specimens counted. In 

 dimensions our species is generally smaller than R. lewisi and more 

 nearly equal in the two diameters. A typical pedicle valve (in mold) 

 measures length 15 by 15 mm. A brachial valve (mold of interior) 

 from the same beds (AI1331.9) measures length 11 width 15 mm. 

 Another pedicle (mold of exterior) measures 12 by 16 (]\il206). 



Davidson's figures of R. lewisi measure: Figure 25, 17 by 20 mm.; 

 figure 26, 30 by 38 mm. (magnified); figure 28, 12 by 12| mm. Our 

 specimens are all in condition of molds of either exterior or interior 

 and are more or less distorted by pressure in several cases. 



The two short dental lamellae of the pedicle valve and the median 

 septum divided posteriorly to form an elongate cavity, are as in Cama- 

 rotoschia and are very similar to that expressed in Camarotoschia 

 eximia Hall of the Devonian. These characters were evidently 

 referred to in his description of Rhynchonella lewisi and quoted by 

 Davidson.' 



Formaiion and locality. — Pembroke formation, gray shales out- 

 croppuig on northern shore of Leighton Cove at end of the promon- 

 tory of Pembroke To^vnship, Washington County, Maine (loc. 5.3.8). 



Coty pes. —Cut. Nos. 58962, 58963, U.S.N.M. 



Genus LINGULA Bruguiere. 

 ' LINGULA SCOBINA, new species. 



Plate 30, fig. 18 (enlarged 3 diameters). 



Cf. 1839. Lingula lewisii Sowerby, Sil. Syst., p. 615, pi. 6, fig. 9. 



Cf. 1866. Lingula lewisii Sowe-rby, Davidson, Brit. Sil. Brae, p. 35, pi. 3, figs. 1-6. 



This species in size and form agrees very closely with Davidson's 

 interpretation of Sowerby's species L. lewisii ^ but the surface of one 



1 Brit. Sil. Brach., p. 180, pi. 23, figs. 2^28. 2 Idem, p. 180. 3 Idem, p. 35, pi. 3, figs. 1-6. 



