950 DR F. R. C. REED ON THE 



Cyclospira ? diversa, sp. nov. 

 (Plate XXIV, figs. 37-43.) 



1883. Rhynchonella portloclciana, Davidson (pars), Mon, Brit. Foss. Brack., vol. v, Silur. Sttppl., p. 159, 

 pi. x, fig. 13 (non figs. 12, 14). 

 Non 1868. Rhynchonella portloclciana, Davidson, op. cit., vol. iii, pt. vii, p. 189, pi. xxiv, figs. 23-25. 



Shell subpentagonal to subtriangular, widest towards front, unequally biconvex. 

 Pedicle-valve convex, highest along middle, subcarinate, with short angular or sub- 

 angular median sinus more or less developed and widening anteriorly ; beak rather 

 elevated, pointed, slightly incurved, with small false area below ; interior of valve 

 with pair of short thin slightly divergent dental plates. Brachial valve with median 

 portion of valve somewhat flattened and anterior portion depressed into wide indefinite 

 shallow sinus holding short narrow median fold about one-third to one-fourth the 

 length of valve ; lateral edges of valve somewhat flattened at right angles to 

 plane of valves ; interior of valve with small thick hinge-plate, cleft in half 

 down the middle, and with long thin median septum extending about half the 

 length of the shell. Surface of shell marked by rather strong lamellose concentric 

 growth-lines. 



Dimensions. — Length, 5-6'0 mm. ; width, 4-5 '5 mm. 



Horizon. — Balclatchie Group. 



Localities. — Ardmillan, Balclatchie. 



Remarks. — This small shell seems much like Cyclospira bisulcata, Emmons,* but 

 it has the small divided hinge-plate of Atrypa exigua, Hall,f which Hall and Clarke 

 put into a distinct genus termed Protozyga.\ Both of these occur in the Trenton 

 Limestone. The internal median septum in the brachial valve and the external 

 characters agree better with the first named, but the hinge-plate with the last 

 mentioned species. 



In all the Ardmillan specimens the pedicle-valve is scarcely at all carinated, and 

 the median groove is only developed in the anterior portion of this valve. One of 

 Davidson's specimens (op. cit., fig. 13) from the mudstone of Balclatchie has a 

 brachial valve precisely similar to the type from Ardmillan, but his other figured 

 specimen (op. cit., fig. 12) is quite distinct in character, having a much longer narrow 

 median fold in this valve, and its true reference is doubtful; it occurs in the Bal- 

 clatchie conglomerate. The typical form of this new species is totally distinct from 

 the Kildare " Rhynchonella" ' portlockiana, Davidson. Crushed and imperfect specimens 

 may be confused with Camarella cuneatella, C. Conybearei, C. balclatchievsis, and 

 C. Thomsoni. The generic reference must be considered extremely doubtful. 



* Hall and Clarke, op. cit., Brack, ii, p. 146, pi. liv, figs. 38-40. 



t Hall, Palxont. N.Y., vol. i, p. 141, pi. xxxiii, figs. 6a-d. 



J Hall and Clarke, op. cit., Brack, pp. 149-151, pi. liv, figs. 47, 48. 



