﻿ADDENDA. 



189 



take the present opportunity of stating that in no instance does it appear certain that 

 an example of T. excentrica has occurred in a higher position" than the Blackdown Green- 

 sand. 



Trigonia debilis, Lye, sp. nov. PI. XL, figs. 8, 8 a (Glabra?). 



Shell small, subovate, moderately convex, umbones pointed, produced, antero-mesial ; 

 costse upon the sides of the valves, depressed, rounded, very closely arranged, horizontal, 

 or transverse, each having an undulation and becoming smaller posteally where their 

 extremities are suddenly turned upwards, meeting the divisional line of the valve at a 

 considerable angle. The small posteal slope has the costellse crowded, transverse, and 

 scabrous. 



The single specimen figured is broken at the siphonal and lower borders ; the height 

 and length are nearly equal, or 5 lines. The costse are thirteen in number, but apparently 

 five others would be required to render the shell perfect to the apex. 



Probably this is only the young condition of a much larger species ; it has some 

 resemblance to young shells of the Glabra, but is quite distinct from either of the known 

 Greensand species in their young states. 



Collected by Mr. Meyer in the bed No. 10 of the Chloritic Marls of Dunscombe 

 Cliffs. 



Trigonia crenulifera, sp. nov. PI. XL, figs. 1, 1 a, 1 b, 7, 9, 9 a (Scabr^e). 



Shell near to the general figure of T. scabricola, but shorter and wider, or more 

 expanded posteally ; the umbones are remarkable for their great elevation and their 

 recurvature ; the anterior side is very short, but is curved elliptically with the lower 

 border ; the anterior face of the shell has little convexity with considerable breadth. The 

 hinge-border is concave and short ; the escutcheon is very large and concave, its borders 

 are raised ; it is traversed transversely by a series of scabrous costellge which are not 

 altogether regular and have their direction somewhat oblique ; they curve irregularly 

 where they pass across to the area, which has greater breadth than in species generally of 

 the aliformis group ; it has much convexity, is conspicuously bipartite, its boundaries, 

 separating it from the escutcheon and from the sides of the valves, are well defined ■ it 

 has a deep mesial furrow which interrupts a series of prominent crenulated costellse which 

 are disposed somewhat irregularly or nearly in zigzag order ; in the adult condition the 

 posteal portion of the area widens and becomes more flattened ; the costelta are ultimately 

 replaced by irregular transverse plications. 



The sides of the valves are covered by a very numerous and closely arranged series of 



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