938 DR F. R. C. REED ON THE 



our Craighead shell. The definition of Pr. nasuta given by M'Coy was incomplete, 

 and has been here revised ; but his original specimen still is the best-known example 

 of the species. 



Protorhyncha sp. 



(Plate XXIII, figs. 24, 25.) 



There is another shell from the Stinchar Limestone which closely resembles 

 Protorhyncha altilis (Hall) * of the Chazy Limestone. It possesses a very globose 

 shell like Wilsonia Wilsoni ; there are about 24-25 equal rounded radii, on the 

 surface, 7 or 8 of which lie on a scarcely perceptible broad undifferentiated fold on 

 the brachial valve, and a corresponding number in an equally weak sinus of the 

 opposite valve. The incurvature of the beaks, the impressed lateral false areas, the 

 ribbing and general aspect of the shell so closely agree with Pr. altilis that its 

 specific identity may even be suspected ; but the specimens are too poor for satis- 

 factory identification, and only one brachial valve from Craighead and a pedicle- 

 valve from Minuntion are known to me. 



Dimensions. — Brachial valve, length, 13'0 mm. ; width, c. 13'0 mm. 



Horizon. — Stinchar Limestone Group. 



Localities. — Craighead, Minuntion. 



Genus Orthorhynchula, Hall and Clarke. 



Orthorliynchula sub-borealis (Davidson). 



(Plate XXIII, figs. 26, 27.) 



1883. Rhynclionella sub-borealis, Davidson, Mon. Brit. Foss. Brack., vol. v, Silur. Suppl., p. 149, pi. x, 

 figs. 5, 6. 



Shell transversely elliptical, gently biconvex, rarely swollen ; hinge-line straight, 



about three-fourths the width of shell. Pedicle-valve with rather prominent 



elevated slightly incurved beak, with triangular concave hinge-area below (( and 



delthyrium covered by pair of deltidial plates) ; median sinus moderately dee]) to 



shallow, widening anteriorly, with sides sloping and floor bearing 2-4 subangular 



subequal ribs ; lateral lobes with 5-7 rather larger or subequal subangular ribs 



straight or gently curved back. Brachial valve deeper than pedicle-valve, with 



smaller low inconspicuous incurved beak and very narrow hinge-area ; median fold 



rounded, more or less distinctly elevated, rising anteriorly, less than one-third width 



of shell on front margin, composed of 3-4 subangular equal ribs ; lateral lobes gently 



convex, bearing 5-7 straight or slightly curved equal subangular ribs. 



Dimensions. — 



(1) (Davidson's tig. 5.) (2) (Davidson's fig. (J.) 



Length . . . . .14*5 12'0 mm. 



Width 18*5 15-0 mm. 



Thickness .... 14*0 8 '5 mm. 



* Hall, Pal&ont. New York, i, 1847, p. 23, pi. iv bis, figs. 9a~d : Hall and Clarke, op. cit., Brach., ii, p. 181. 





