274 PALEONTOLOGY OF NEW YORK. 



Genus STREPTIS, Davidson. 1881. 



PLATE XI C, FIGS. ;!3-39. 



1848. Terebratula, Davidson. Bull. Soc. Geol. de France, 2nd sei-., torn, v, p. 331, \i\. Hi, tig. 33. 



1859. Rhynohonella, Salter. In Murchison's Silui-ia, p. 250. 



1860. Spirigerina?, Lindstrom. Gotland's Brachiopoder, p. 364. 



1867. Atrypah Davidson. British Silui-ian Bi'achiopoda, p. 141, pi. xiii, figs. 14-22. 



1879. Atrypa'?, Barrandb. Systeme Silurien ilu Centre de la BohSme, vol. v, \>\. 83. 



1881. Stveptis, Davidson. Geolog-ical Magazine, vol. viii, p. 150, pi. v, fig. 13. 



1883. 8treptis, Davidson. British Silurian Brachio|H)da, Suppl., p. 39. 



From what is known of the single species of this genus, S. Grayi, from the 

 Wenlock limestone, it would appear that its internal characters are essentially 

 similar to those of Triplegia. Mr. Davidson says that he was unable to deter- 

 mine the precise character of the cardinal process, but an imperfect interior, 

 illustrated upon plate xiii, tig. 21, of his Silurian Monograph, shows that it was 

 erect, though it appears to have been broken at the point of bifurcation ; the 

 short spiniform crura are also very distinctly seen, and upon careful examina- 

 tion of the specimens short dental plates can be seen in the pedicle-valve. 

 The exterior of the shell, however, is very peculiar in its bilateral asymmetry, 

 the existence of a sinus on each valve, and in the broad free frills at the con- 

 centric growth-lines.* In respect to its asymmetry the species, as already 

 observed, bears very much the same relation to Triplegia as the Mimulus Wald- 

 ronensis, from the Niagara fauna in Indiana, does to typical forms of the genus 

 Mimulus. The combination of these features with the surface ornamentation, 

 and the very small size of the species, will form a valid ground for the recogni- 

 tion of Streptis as a group subordinate to Triplegia. 



* This feature is more extravagantly developed in the Bohemian species according to the figures given 

 by Barrande (SystJ:me Silurien, vol. v, pi. 83, figs. 2, 3a, 3d), than in the English forms figured by David- 

 son. The Bohemian specimens are from Etage E^. 



