940 DR F. R. C. REED ON THE 



a transverse globose shell measuring about 8 mm. long, 10 mm. wide, and 6'5 mm. 

 in depth ; the valves are deeply re-entrant, the tongue of the sinus being long and 

 strongly bent down, and the union of the valves forms deep zigzags ; there are 2 ribs 

 in the sinus and 3 on the fold, with 3 on each lateral lobe, the lateral rib bound- 

 ing the sinus on each side being more elevated and prominent at its anterior end. 

 The second larger shell is poorly preserved, but seems similar to the above described 

 one. The third and largest, measuring 11 mm. long, 15 mm. wide, and 9"5 mm. 

 deep, is similarly transverse and globose, with deep re-entrant valves, but there seeni 

 to be 4 ribs in the sinus, and they are of smaller size than the 5 ribs on each lateral 

 lobe ; the characters of the brachial valve are not well preserved. Probably this 

 shell is the adult form of the species. It may be compared with Rh. inwquivalve, 

 var. laticostata, Winchell and Schuchert.* 



Horizon. — Whitehouse Group. 



Locality. — Shalloch Mill. 



Rhynchotrema' 1 . girvanense (Davidson, emend.). 

 (Plate XXIV, figs. 3-6.) 



1883. Rhynchonella girvaniensis, Davidson, Mon. Brit. Foss. Brack., vol. v, Silur. Suppl., p. 155, 

 pi. x, fig. 26. 

 ? 1883. Rhynchonella nucula, var. ?, Davidson, ibid., pp. 157, 225, pi. x, fig. 30; pi. xi, fig. 24. 



Shell subcircular to transversely elliptical, subglobose. Pedicle-valve with high 



prominent slightly incurved acutely pointed beak ; shoulders sloping at about 90° ; 



median sinus shallow, rapidly increasing in width to front margin, where it measures 



more than one-third the width of valve ; floor of sinus flat, carrying 3 equal subangular 



ribs ; sides of sinus steep, low ; lateral lobes Rearing 4-6 subequal ribs, of which those. 



bordering sinus are somewhat elevated at anterior ends. Brachial valve convex, 



swollen, with low inconspicuous incurved beak ; low rounded median fold composed 



of 3 subangular ribs ; lateral lobes bearing 4-5 similar subangular ribs. Interior 



with median septum about one-third length of valve. 



Dimensions. — 



(Davidson's fig. 26.) 



Length ........ 7'00 mm. 



Width 875 mm. 



THickness . . . . . . . c. 6*00 mm. 



Horizon. — Balclatchie Group (conglomerate). 



Locality. — Balclatchie. 



Remarks. — Davidson's description, consisting of less than two lines, is quite 



inadequate as a specific diagnosis, and his figure is a restoration of the specimen. 



None of the specimens available are well preserved. The form which he termed 



Rh. nucula, var. ?, differs in having rather finer and more numerous ribs, 4 existing 



* Winchell and Schuchert, Pal&ont. Minnes., vol. iii, p. 461, pi. xxxiv, figs. 26-29. 



