Vol. 62.] IN THE CAEBONIFEEOTTS EOCKS AT BUSK. 311 



Steingothyeis subconica (Martin). (PI. XXX, fig. 7.) 



Characters of the pedicle-valve. — Form pyramidal. The 

 area is a plane-triangle ; the beak marks the apex of the area, but 

 does not curve over it ; deep angular sulcus, without ribs ; the flanks 

 are ornamented by seven or eight sharp, perfectly-radial ribs, which 

 have a strong laminose concentric ornament. 



This shell is a characteristic fossil in the Cyathaxonia-Be&s of 

 the Rush sequence, and is apparently not uncommon. The speci- 

 mens from Rush appear to agree exactly with Martin's type-figure. 1 

 A similar form (which, however, differs in the depression of the 

 mesial fold) is figured by Davidson 2 from Wetton, and, judging 

 from the numerous specimens in Dr. Wheelton Hind's collection, 

 the form is common at Castleton. 



In the South- Western Province only two specimens of a Syringo- 

 thyris have yet been discovered in the top beds, and these must both 

 be named Syringothyris cf. cuspidata. 



JSyringothyris cf. laminosa (Z 2 to S,) differs markedly in its 

 regularly-concave area (it has consequently a strongly Spiriferina- 

 like aspect). 



Maetinia glabea (Martin). 



This is an abundant fossil in the Curkeen Limestone. The 

 predominant form is more transverse than Martin's type-figure 

 (op. supra cit. pi. xlviii, figs. 9 & 10), and agrees more closely with 

 the form figured by Davidson (op. supra cit. pt. v, pi. xi, fig. 3). 



In the South-Western Province, Martinia glabra is only found 

 in D 2 , where it is locally very abundant (Oystermouth Beds, 

 Gower) ; it is also very common in the uppermost Avonian of the 

 Midland area. 



There is, in the Curkeen Limestone, a very striking convergence 

 between Athyris glabristria and Martinia glabra, both of which 

 are extremely abundant there. They both possess the same contour 

 and general convexity ; the same broad, gentle, mesial swelling 

 and shallow mesial depression ; and the same broad and rounded 

 beak-region. The widely-distinct generic characters can, however, 

 always be made out by careful examination. 



The test of the Athyris is completely fibrous, and has a ' matt ' 

 surface ; that of the Martinia has a translucent lustre, due to the 

 character of the minutely-punctured outermost layer. 



When the beak is completely exposed, the Martinia has a tri- 

 angular area and a short, straight hinge-line ; the Athyris has no 

 area, and the hinge-line is broadly angled. 



If the test be removed from the rostral region, the Martinia is 

 seen to have no dental plates ; but the cast is marked by several 

 very strong, sharp, radiating ridges, which stand up like septa. The 



1 ' Petrificata Derbiensia ' 1809, pi. xlvii, figs. 6, 7, & 8. 



2 'Monogr. Brit. Foss. Brachiop.' (Palseont. Soc.) Appendix, 1863, pi. hi. 



fig. 4. 



