Vol. 65.] ROCKS OP IHE TOTJRMAKEADY DISTRICT. 151 



the Irish Llandeilo. The presence of the grooved area inclines me 

 to place this shell in the genus Acrotreta, as now understood. 1 



Camerella thomsont (Davidson). 



The fossil which has been referred to this species 2 occurs rather 

 frequently in both the Tourmakeady and the Shangort Beds, but 

 it is usually in a poor state of preservation. Its external resem- 

 blance to Wiynchonetta digitata (Leucht.) 3 of the Expansus- Shales 

 of Scandinavia is deserving of notice, but we are without knowledge 

 of the internal characters of either species. C. ihomsoni occurs 

 typically in the Craighead Limestone of Girvan. 



Streptis aeeinis, sp. nov. (PL VI, figs. 14 a & 14 b.) 



Description. — Shell transversely oval, nearly twice as wide 

 as long, symmetrically bilobate. Pedicle-valve moderately convex, 

 composed of two equal rounded lobes, divided by a shallow median 

 longitudinal sulcus which causes the central emarginatiou of the 

 anterior border ; beak somewhat swollen, small, incurved, rising 

 a little above the straight hinge-line ; hinge-area not preserved ; 

 hinge-line rather less than the width of the shell. Surface of valve 

 marked by about twenty-five regular, equidistant, and subequal, 

 closely-placed, low, rounded, concentric ridges following the outline 

 of the shell, and separated one from the other by sharply impressed 

 lines ; ornamentation of ridges consisting of small, round, sub- 

 equal, pointed tubercles, rather widely separated and more or less 

 regularly disposed in lines radiating from the beak, with some 

 minute granules occasionally interspersed. 



Interior of pedicle-valve with a narrow, transverse, umbonal ridge 

 or lamella cutting off a small umbonal cavity and connecting the 

 small pair of teeth ; a thin median septum also partly divides the 

 umbonal cavity longitudinally. In front of the transverse ridge lies 

 a pair of bilobed, sub-pyriform, slightly divergent muscle-scars (di- 

 ductors) extending nearly half the length of the valve, rather more 

 deeply impressed in front than behind, and separated for their whole 

 length by a partly-fused pair of narrow, linear adductor-impressions, 

 which anteriorly diverge slightly and expand into small, short, 

 suboval scars lying in front of the diductors. Three pairs of short 

 vascular sinuses, deeply excavated at their origin, diverge from the 

 sides and front of the diductor-scars. 



Dimensions. — Length of pedicle-valve = about 6*5 millimetres; 

 width of the same = about 11 mm. 



Remarks. — There is available for examination one nearly 

 perfect pedicle-valve of this brachiopod, represented by the external 

 impression of the shell and the internal cast of the same individual, 

 together with several fragments of valves. All come from the same 



1 C. D. Walcott, Proc. U.S. Nat. Mus. vol. xxv (1903) pp. 577-601 ; and 

 Smithsonian Miscell. Coll. vol. liii (1908) no. 1811, p. 146. 



2 T. Davidson, ' Monogr. Brit. Foss. Brach.' vol. iii, p. 186 & pi. xxiv, fig. 18, 

 Palffiont. Soc. vol. xxii (1868). 



3 W. C. Brogger, ' Die Silur. Etagen 2 & 3 ' p. 52 & pi. xi, figs. 2 a-2 c. 



