TEREBRATULINA. 11 



dredging off Skye; also in thirty fathoms off Croulin Island, near Skye, by Mr. M'Andrew; 1 

 and lately at the Haaf, or deep-water fishing-grounds of Zetland, by Mr. Barlee. It may 

 be said to be one of our rarest little Brachiopoda, both in the recent and fossil states. 

 Plate I, fig. 2, one of the recent shapes of this shell. 



„ fig. 2 a , enlarged figure. 



„ fig. 13, nat. size of the Crag specimens, from Mr. J. Wood's collection. 



„ fig. Vd abcd , enlarged illustrations. 



Genus — Terebratulina, D'Orbigny. 1847. 



Shell inequivalve, ovate, circular or irregularly pentagonal, variable at different stages 

 of growth. Valves convex or depressed; beak more or less produced, and obliquely 

 truncated by the foramen which is excavated out of the substance of the beak, completed 

 by the umbo and by two small rudimentary, lateral, obsolete, deltideal projections, no area 

 or distinct lateral ridges ; the smaller valve deepest at the umbo, with two more or less 

 developed auricle expansions. Structure punctuated ; surface either minutely striated, 

 plaited, or costellated, articulating by the means of two teeth in the larger, and 

 corresponding sockets in the smaller valve. Apophysary skeleton short, not exceeding a 

 third of the length of the shell, and formed of two short stems, simply attached to the 

 extremity of the socket ridges, which, after converging, are united by a lamella, in the 

 shape of a small, square, tubular ring, bent upwards in front, to the sides of which are 

 fixed the free fleshy arms of the animal, these extending to near the front margin, bent 

 back in the shape of a loop, the outer edges being covered by long cirri ; body of the 

 animal small, the edges of the mantle free, pedicule muscles very short ; dimensions rarely 

 exceeding one inch and a half. 



Obs. The separation of the shells forming this genus from Terebratula is due to 

 M. D'Orbigny, who pointed out the difference of their respective apophysary skeletons. 

 We differ, however, from that author, when stating that this genus is deprived of 

 deltidium ; it generally is rudimentary, small, and lateral, but in some species, as in 

 T. substriata of Schlotheim, the deltidium is large and almost complete. M. D'Orbigny is 

 likewise in error in the statement, in his 'Pal. Prancaise Ter. Cretaces,' vol. iv, p. 58, that 

 the genus Terebratulina appeared for the first time in the Cretaceous period. I am per- 

 fectly well acquainted with two forms of the genus in the Oolitic period, one of which is 

 the Terebratulina substriata of Schlotheim, placed by M. D'Orbigny 2 among the Terebratula. 



1 These specimens have been presented by Mr. M'Andrew to the Museum of Practical Geology, where 

 they were pointed out to me by Professor Forbes ; in size and shape they quite agree with those from 

 the Crag. 



2 'Prodrome,' vol. ii, p. 24, 1850. (This species belongs to the Cor. Rag: has been figured by 

 Zieten in 1832, under the name of T. striatula. It is not the same as Sowerby's or Dr. Mantell's species, 

 bearing that appellation.) 



