166 SUPPLEMENT TO THE 



64. Stricklandinia (?) Balcletchiensis, Dav. Sil. Sup., PI. IX, figs. 27 to 29. 



Shell marginally sub-pentagonal, longer than wide ; ventral valve moderately convex 

 with about six angular ribs, commencing at about one third of the length of the shell, 

 and occupying the central third of the breadth of the valve ; lateral portions or lobes 

 smooth ; beak incurved ; fissure triangular, large ; dorsal valve not known. 

 Length 1 J inches, breadth 1 inch. 



Obs. — Of this remarkable species Mrs. R. Gray has found nine fragmentary or 

 incomplete ventral valves only. They all presented exactly the same character. The 

 internal cast of the ventral valve shows a small V-shaped chamber. The dorsal valve 

 not having been found, and nothing being known of its interior arrangement, this form 

 is provisionally classed with StricJdandinia on account of its small V-shaped chamber, 

 although no species of the genus is known to occur so low down in the geological scale. 



The specimens were all procured from the Balcletchie conglomerate, or Upper Llan- 

 deilo, at Balcletchie in Ayrshire. 



Genus — Lept^na, Dalman, 1827. 



The species composing this genus are elegant in shape and delicate in sculpture. 

 Some ten or twelve British species have been described. They are far less specifically 

 numerous than are those classed under Strophomena^ but they enjoyed a similar 

 and even more extended vertical range. Some of the species are so variable in shape 

 that they are difficult to distinguish, and several of them seem almost to pass one into 

 the other. 



C5. Lept^ena segmentum, Angelin var. cormda, Dav. Sil. Sup., PI. XII, figs. 1, 2, 3. 



Shell small, concavo-convex, wider than long, transversely sub-pentagonal, broadest 

 at the hinge-line ; cardinal extremities prolonged and angular ; dorsal valve convex, and 

 divided into three parts or lobes by two large angular ribs, projecting beyond the ante- 

 rior semi-circular curve of the valve ; the central lobe is either uniformally convex or 

 divided by a median rounded rib of much smaller size than the lateral ones ; beak much 

 incurved, area narrow, divided by a small fissure partly arched over by a deltidium. 



