294 
PALAEONTOLOGY OF NEW YORK. 
1884. 'TtrtbyatuLa, Whitu. Thirteenlli Kept. State Geol. Indiana, p. 137, pi. xxxii, figs. 17-19. 
1884. Terebratula, Walcott. Monogr. U. S. Geol. Survey, vol. viii, p. 224. 
1884. Dielasma, Davidson. British Fossil Brachiopoda; General Summary, p. 411. 
1887. Dielasma, de Koninck. Faune du Calcaire Carbonifei-e de la Belgique, pp. 5-31, pis. i-viii. 
1889. Terebratula, Nettblroth. Kentucky Fossil Shells, p. 155, pi. xvi, tigs. 20-22. 
1890. Terebratula (Cryptonella), Calvin. Bull. Lab. Nat. Hist. State Univ. Iowa, ji. 174, pi. 3, fig. 4. 
1893. Dielasma, Beecher aud Schuchbrt. Proc. Biol. Soc. Washington, vol. viii, pp. 71-78, pi. x. 
Some years before the introduction of this term its distinguished author had 
applied Phillips’ name, Epithyris, to certain Permian species {Terebratulites elon- 
gatus, Schlotheim, type) which he found to differ from Terebratula, in the sense in 
which the term was then current, in their “ prominent dental plates and trans¬ 
versely semi-elliptical moderately recurved loop.” Epithyris, as used by Phillips, 
has no significance as a generic term; whatever value it might have was thus 
given it by King, but the author subsequently decided to discard the term and 
introduce a new one, Dielasma. The name has not been widely adopted, though 
this fact appears to have come, less from any objection to, or insufficiency in, 
the distinctive characters of the division, than to a general disposition to leave 
all the terebratuloid shells of the Palmozoic with the old genus, Terebratula. 
Waagen has recognized the value of this genus and the usual facility with which 
its species may be recognized. It is not, however, upon the characters given by 
King that we can rely for the distinction of Dielasma from the other palaeozoic 
terebratuloids. In external form, the convexity of both valves is generally well 
developed, and the outline is usually elongate-oval. But in both of these 
respects there is very considerable variation; the development of a median 
sinus on both valves with a plication and groove at the bottom of it, as in the 
Terebratula turgida, Hall, of the Chester limestone, and T. vescicularis, de Koninck, 
of the Coal Measures, produces a form at once suggestive of the typical 
biplicate Terebratula of the Jurassic age. A general depression of the pedi¬ 
cle-valve anterior to the umbo, and a corresponding elevation of the opposite 
valve, appearing first in the Cryptonella Calvini, Hall and Whitfield, of the mid¬ 
dle Devonian, is carried to an extreme in the T. bovidens, Morton, of the Coal 
Measures. 
The apex of the pedicle-valve is closely incurved, so that in adult shells but 
little remains of the deltidial plates. The foramen is large, quite generally 
