66 PALAEONTOLOGY OF NEW YORK. . 



1879. Meristim, Hall. Twenty-eighth Reiit. N. Y. State Miis. Nat. Hist., p. 159, pi. xxv, fig-s. 8-12. 



1881. Whitfieldia, David.son. Geological Magaziiie, new ser., vol. viii, p. l.'J6. 



1882. Meristina, Hall. Eleventh Ann. Kept. State Geologist Indiana, p. 299, pi. xxv, figs. 8-12. 

 1882. Hliitjieldia, Davidson. British Silurian Braohiopoda, Supplement, p. 107. 



1889. Meristina, Nettelroth. Kentucky Fossil Shells, p. 101, pi. xxix, tigs. 7-10. 



1889. Whitfieldia, Beecher and Clarke. Memoirs N. Y. State Museum, p. 73, pi. vii, tigs. 1-3. 



Diagnosis. Shell biconvex, the greatest depths of the valves being subequal. 

 General expression meristoid. The beak of the pedicle-valve is erect in youth, 

 but so greatly incurved at maturity as to totally conceal the foramen and 

 deltidiuni. Cardinal slopes narrow but distinct, forming prominent slioul- 

 ders which may be traced nearly to the middle of the lateral margins. 

 A low, often indistinct median ridge extends from the apex forward ; at 

 about the middle of the shell it is divided by a faint groove, becoming 

 broader toward the margin and continued into a subnasute extension. 

 Lateral slopes scarcely depressed. 



The brachial valve also bears a low median ridge, wliich manifests itself 

 most conspicuously over the anterior portion of the sliell. 



On the interior of the pedicle-valve the teeth are conspicuous and are sup- 

 ported by thin plates, which extend to the bottom of the valve and are produced 

 forward to form the lateral boundaries of the muscular area. Between the 

 posterior portion of these plates lies the deep scar of the pedicle muscle, which 

 is separated from the elongate and radially striate diductor impression by a 

 prominent callosity. 



In the brachial valve the hinge-plate is deeply divided in the middle by a 

 narrow sulcus, the two lateral lobes being elevated, and supporting the crural 

 bases. The plate is thickened on the under side and supported by a median 

 septum, which extends for one-half the length of the valve. The crura are 

 short and straight, and the primary lamellae of the spiral ribbon originate from 

 them at a sharp angle, diverge laterally as they turn downward, passing over a 

 portion of the secondary volutions, approach each other toward the middle 

 of their length, nearly meeting at the anterior edge of the median septum, 

 thence again diverging to their anterior recurvaiure. The secondary volu- 

 tions do not follow precisely the curvature of the primary lamellse and the 

 resultant cones at maturity have a gracefully undulated surface. The loop 



