NO. 1985. NEW SPECIES OF SILURIAN FOSSILS— WILLIAMS. 347 



MODIOLOPSIS LEIGHTONI var. QUADRATA, Williams. 

 Plate 31, figs. 12, 13. 



This variety has the surface markings very similar to and varying 

 as in M. leightoni but it differs from the typical form in its greater 

 height. The antero-posterior diameter exceeds the height by about 

 a third, whereas in the typical form the length is about twice the 

 height. The specimens figured do not express the average size. 

 Figure 13 represents the largest specimen in the series and fairly 

 expresses the general form, except that the surface is distorted by 

 some hard fragment underlying it. Figure 12 has the front side a 

 little shorter than usual, giving the vertical margin greater obliquity 

 than the species generally exhibits. It is also somewhat crushed 

 irregularly. 



The two specunens (Cat. No. M1349.7 and M1351.32) give the 

 characters of the variety in its medium expression. Intermediate 

 forms between this and the typical species are also seen in the series 

 from the same locality. 



Formation and locality. — Pembroke formation, in Leighton gray 

 shale member at head of Leighton Cove, Pembroke Township (loc. 

 No. 5.3.8F and M). 



Cotypes.—C&t. No. 58975, U.S.N.M. 



Genus NUCULITES Conrad. 



NUCULITES CORRUGATA, new species. 



Plate 31, figs. 11, 14. 



Shell elongate ovate, thin, about twice as long as high; hinge line 

 nearly straight; front evenly rounded. Posterior end extending 

 backward and subangulate. Beak, within the anterior third of 

 length of shell, but varying in the several specimens. Surface smooth 

 except for faint concentric lines of growth and crossed by several 

 faint radial grooves on the posterior half of the right valve. On the 

 left valve these consist of two umbonal ridges separated by a broad 

 furrow; in one specimen there appears a secondary ridge in middle 

 of the furrow. These radiating ridges and furrows are faintly ex- 

 pressed and are nearly obsolete in some specimens. The clavicular 

 ridge is slender and long, in some specimens reaching beyond the 

 middle. Its inclination varies considerably in the specimens and the 

 proportions of the shell also vary. The differences, however, appear 

 to be due partly at least to distortion during and since fossilization. 



The species resembles Nuculites ohlongatus Conrad, also Beushau- 

 sen's figure 11 on his plate 5 of CucuUela elliptica Mauer. It differs 

 from both in the radiating ridges and furrows and in the subangulate 

 posterior margin. 



Formation and locality. — Pembroke formation, in the Leighton 

 gray shale member at the head of Leighton Cove, Pembroke Town- 

 ship (loc. No. 5.3.8.F). 



Cotypes.—C&t. No. 58976, U.S.N.M. 



