ORDOVICIAN AND SILURIAN BRACHIOPODA OF THE GIRVAN DISTRICT. 899 



imperfect and broken, but the flattening in this region is apparent. In both the orna- 

 mentation is completely different from that of the true Raf. semiglobosina (Dav.) 

 (see p. 869). 



The ribbing and shape of Str. Nicholsoni recall some species of StropJiomena 

 from the American Ordovician (e.g. Str. 'planoconvexa, Hall,* and Str. sulcata, 

 Verneuil f ), but the strongly swollen beak, the apparently denticulated hinge-line, and 

 the reversed convexity of the valves mark it off from, all of these species and from this 

 minis. It is named in honour of Professor Alleyne Nicholson, whose monograph 

 on the Grirvan fossils, in collaboration with R. Etheridoe, jun., is well known. 



Stropheodonta ? Waltoni (Davidson) ? 



1 1847. Leptxna Waltoni, Davidson, London Geol. Journ., vol. i, p. 56, pi. xxvi, fig. 3. 

 1 1848. Leptsena Waltoni, Davidson, Bull. Soc. Geol. France, ser. 2, vol. v, p. 317, pi. iii, fig. 6. 

 1883. Strophomena Waltoni, Davidson, Mon. Brit. Foss. Brack., vol. v, Silur. SuppL, p. 195, 

 pi. xvi, fig. 1. 



There is only one poor external cast of one valve of this species, and Davidson's 

 figure is more or less a restoration. Davidson's identification with Str. Waltoni is 

 uncertain, though the shape of the shell is similar to the type of Str. Waltoni from 

 the Wenlock Shale of Falfield,| but the ornamentation is not clearly preserved. The 

 hinge-line is apparently denticulate, and the shell may be probably referred to the 

 genus Stropheodonta. It is possible that this specimen may belong to the species 

 Stroph. arenacea, Salter, which has been above described from Camregan. 



Horizon. — Camregan Group. 



Locality. — Cuddystone Glen. 



Stropheodonta sp. 



(Plate XVIII, figs. 9, 10.) 



There are some fragmentary shells from Mulloch Hill in Mrs Gray's collection 

 which" seem to possess many of the characters of Str. corrugatella (Dav.) of the 

 Upper- Ordovician, but on account of certain differences it does not seem possible to 

 include them in this species. Thus the shell is subquadrate in form, with small 

 pointed ears, and it is rather suddenly arched down at about two-thirds its length, 

 though not provided with a flattened disc or distinct geniculation. The character- 

 istic ornamentation is mainly limited to the portion of the shell which is not bent 

 down, the latter portion being only covered with the radiating primary riblets with 

 the wide interspaces showing 2-3 finer radial lines. These characters resemble those 

 of Str. Patersoni, HallJ of the Devonian of North America rather than the typical 

 Str. corrugatella (Dav.). One internal cast of a pedicle-valve, somewhat broken and 



* Fokrste, Bull. Seient. Lab. Denison Univ., vol. xvii, 1912, p. 54, pi. i, figs. 1a-e, 2a, b. 

 t Ibid., p. 102, pi. i, figs. 4a-o ; pi. xi, fig. 2. + Davidson, op. cit., vol. iii, p. 310, pi. xlii, fig. 11. 



§ Hall, Tenth Ann. Rep. New York State Cab. Nat. Hist., 1857, p. 114, figs. 1-5 ; Hall and Clarke, op. cit. 

 Brach., i, 1892, pi. xiv, fig. 15. 



TRANS. ROY. SOC. EDIN, VOL. LI, PART IV (NO. 26). 129 



