918 DR F. R. C. REED ON THE 



incomplete. The true generic position of this shell is certainly in Clitambonites, 

 although we are still ignorant of the internal characters. 



The sharply conical shape of the pedicle-valve, the median sinus on its surface 

 instead of a carina, the inclination of the hinge-area and the wider delthyrium, the 

 more numerous and less regular ribbing distinguish it from Sc. Greenoughi (see 

 p. 920) from the same horizon and locality. 



Genus Hemipronites, Pander. 



Hemipronites carrickensis, sp. nov. 



(Plate XXI, figs. 24-26.) 



1883. Strophomena retroflexa, Salter, Davidson (pars), Mon. Brit. Foss. Brack., vol. v, Silur. Suppl, 

 p. 195, pi. xv, figs. 7-8. 

 Non 1865. Strophomena 1 retroflexa, Salter MS., Cat. Foss. Mus. Pract. Geol, p. 8. 



Shell semielliptical to subquadrate, unequally biconvex ; hinge-line rather less 

 than maximum width ; cardinal angles subrectangular to obtuse. Pedicle-valve 

 deepest at beak, conical, with somewhat flattened surface ; beak forming apex of 

 cone, not incurved, the margins of hinge-area meeting at beak at very obtuse angle 

 (about 130°-140°); hinge-area large, flat, triangular, steeply inclined' to plane of 

 valve, with narrow median delthyrium. Brachial valve gently convex, with weak 

 median depression usually present ; beak small, inconspicuous, not rising above hinge- 

 line ; hinge-area narrow, steeply inclined. 



Surface of valves covered with small rather unequal closely placed rounded thread- 

 like lines increasing in number by intercalation more than once, every second or third 

 or fourth line rather stronger than the others, and all arched back slightly on lateral 

 portions of valves ; 3-4 strong concentric lamellose growth-ridges usually present 

 near margin, and fine concentric striation over rest of surface. 



Dimensions. — 



Pedicle-valve. Brachial valve. 



(1) (2) (3) (4) 



Length. . . . 16*0 15'0 mm. 12"0 12'5 mm. 



Width . . . 20*0 16*5 mm. 15'5 17'0 mm. 



Horizons. — (l) Stinchar Limestone Group ; (2) Balclatchie Group. 



Localities. — (l) Craighead ; (2) Balclatchie (conglomerate). 



Remarks. — The external characters of this shell, in spite of our ignorance of its 



internal structure, are such as to make its reference to the genus Hemipronites * a 



matter of little doubt, and it seems to be related to H. inflexa, Pander, as interpreted 



by Pahlen,! and to H. Giraldi, Martelli.J 



The type of "Strophomena" retroflexa, Salter, to which species Davidson § 



* Hall and Clarke, op. cit., Brach., i, p. 238. 



t Pahlen, Mem. Acad. Imp. Sc. St Petersburg, ser. vii, vol. xxiv, 1877, No. 8, p. 28, t. iii, figs. 1, 2 (cet. excl.) ; 

 Lamansky, Mem. Com. Geol. St Pe'tersbourg (N.S.), xx, 1905, pp. 73, 176. 



\ Martelli, Boll. Soc. Geol. Ital., vol. xx, 1901, p. 305, pi. iv, figs. 7-12. 

 § Davidson, op. cit., vol. iii, p. 298, pi. xlii, figs. 15-17. 





