Wetter — Kinderhook Faunal Studies. 199 



sometimes extended into submucronate points, rounded in 

 front. 



; ' Brachial valve more convex from beak to front than trans- 

 versely. Beak scarcely prominent, slightly projecting beyond 

 the hinge-line. 



" Pedicle valve about twice as deep as the opposite one, 

 regularly arcuate from beak to front, but a little de- 

 pressed near the cardinal extremities. Area large and well 

 defined, delthyrium narrow, beak acute, incurved, and be- 

 coming solidified as the delthyrium is progressively closed. 

 Dental plates strong, projecting a little forward of the hinge- 

 line. From six to eight prominent plications on each side of 

 the mesial fold and sinus, which decrease regularly in size 

 toward the hinge extremities. Sinus rather broad and deep, 

 distinctly defined even to the point of the beak ; a slightly 

 elevated ridge extends along its bottom, and a corresponding 

 depression along the mesial fold. 



" Mesial fold prominent and widely separated from the plica- 

 tions. Surface marked by fine, lamellose, concentric striae, 

 which arch upon the plications and the ridge in the mesial 

 sinus, and doubly arch upon the mesial fold." 



The dimensions of one of the best preserved pedicle valves 

 among the types are: length 111 mm., width along the hinge- 

 line 15 mm., and convexity 6 mm. Another brachial valve 

 is 9i mm. long, 19 mm. wide along the hinge-line, and hns a 

 convexity of 4 mm. 



Remarks. Neither the types nor any authentic specimens 

 of this species have ever been illustrated, and it has often 

 been confused with S. sublexta, a species described by White 

 from the base of the Burlington limestone. This latter 

 species also has never been illustrated, and therefore a figure 

 of the type specimen has been introduced on the plate with 

 S. solidirostris (see Plate XX, fig. 5-6). 8. solidirostris 

 may be recognized by its stronger lamellose lines of growth, 

 and by the slight furrow in the median fold and the corre- 

 sponding elevation in the sinus. 



NUCLEOSPIRA BAKRIST White. 

 PI. XX. f. 7-11. 



Original description. " Shell transversely oval, gibbous, 

 becoming ventricose with age. Hinge-line short, surface 



