SPIRIFERID^. 



141 



Atrypa? Grayii, Davidson. PI. XIII, figs. 14—22. 



Terebeatula Geayii, Davidson. Bull. Soc. Geol. France, 2nd ser,, vol. v, p. 331, 



pi. iii, fig. 33, 1848. 

 Rhynchonella — Salter. Siluria, p. 250, Foss. 57, fig. 3, 1859. 

 Spieigeeina? — Lindstrom. Gottland's Brachiop., p. 364, 1860. 



Spec. Char. Shell small, transversely oval, irregular, and abruptly twisted, from one 

 half of the shell being more elevated than the other. Valves almost equally convex 

 without fold or sinus, but with a median depressed line only ; beak of ventral valve 

 small, moderately incurved, and truncated by a minute circular foramen, which is 

 separated from the hinge-line by a small narrow deltidium in one piece ; beak-ridges 

 sharply defined, leaving between them and the hinge-hne a narrow triangular area. 

 Surface ornamented by concentric ridges, from which rise narrow (frill-shaped) projecting 

 laminae, longitudinally plaited. Interior not known ; excepting the cardinal process in 

 the dorsal valve. 



Length 5, width 7, depth 3 lines. 

 Obs. This strangely shaped shell, of which I have seen about forty specimens, 

 does not appear to have exceeded the dimensions above given, and is generally much 

 smaller. It constantly assumes the same character, that is to say, having always its 

 right or left half twisted higher or lower than the other ; and consequently both valves 

 are longitudinally divided along the middle by a sharply curved line. When well 

 preserved, the surface exhibits a variable number of rows of projecting concentric laminae, 

 as in Atrypa reticularis, but much narrower ; the surface is smooth in worn specimens 

 only. It is well known that some species of Rhynchonella, and of other genera, at 

 times or even normally assume a similarly twisted appearance. My endeavoui's to 

 procure specimens showing internal characters have proved fruitless ; and I cannot 

 therefore determine exactly the genus. It is evidently not a Terehratula, for its shell is 

 fibrous and impunctate ; its surface-ornament is not that of a Rhynchonella. Lindstrom 

 has placed it (with a mark of interrogation) in Atrypa {Spiriyerina), where we may 

 provisionally leave it. The hinge and cardinal process are peculiar ; the last projecting 

 considerably, as seen in fig. 21. Whether or not it possessed spiral lamellae is uncertain.^ 



Position and Locality. Atrypa ? Grayii has been hitherto found in the Wenlock 

 Limestone only. It occurs at Hay Head, near Walsall ; some rare specimens have also 

 been procured near Dudley. 



Dr. Lindstrom finds it at Wisby, in the Island of Gothland, and there it appears to 

 be rare. 



1 Prof. Hall, to whom I sent specimens of this species, thinks that spires will be ultimately found ; 

 but that it is neither a Rhynchonella, an Atrypa, nor an Athyris, though it may be alUed to the latter ; it 

 is 80 different from any American forms. 



