ADDENDA. 205 



Trigonia costigera, Lye. Plate XLI, fig. 17 (Mould). 



I am indebted to Mr. C. J. A. Meyer, F.G.S., for information respecting this 

 imperfectly known species discovered by that gentlemen in the Chloritic Marl rocks of the 

 South Devon Coast, near to Beer Head; the bed is No. 10 of Mr. Meyer's classified 

 section. Several examples have been observed larger than our Trigonia on Plate XLI ; 

 these, however, consisted only of impressions of the costse. The small mould herewith 

 figured is the only one hitherto obtained ; it has some small portion of the shell attached, 

 including three short, horizontal costse upon the anteal portion of the valve ; these have 

 some traces of crenulations. The figure is ovately subtrigonal, moderately convex pos- 

 teally and depressed anteally ; there are some obscure indications of a marginal carina ; 

 the umbones are submesial, prominent, and pointed ; the unusual shortness of the form 

 is remarkable, the length and height being nearly equal ; the abruptness of the posterior 

 slope chiefly contributes to this peculiarity. These few features are insufficient to cha- 

 racterise the species, and its sectional position is somewhat doubtful. I am inclined to 

 arrange it with that group of the Scabrcs which includes T. sulcataria, T. pennata, T. 

 Meyeri, and T. Nereis, which have the posteal portions of the costse small, sometimes ill 

 defined, and bent upwards perpendicularly or at right angles to their anteal portions. 

 ]S[one of these features are preserved upon our specimen, but in the absence of any well- 

 grounded expectation that better specimens will be obtained I have ventured to figure 

 this very defective shell. 



Trigonia Blakei, Li/c, sp. nov. Plate XLI, fig. 4. 



Shell with the general figure ovately oblong ; umbones prominent and pointed, 

 placed at the boundary of the anteal third of the valve ; posteal slope straight and 

 lengthened ; borders of the valves elliptically curved. Area moderately wide, somewhat 

 concave, distinctly bipartite, with three slightly developed tuberculated caringe. Escutcheon 

 small and depressed. Costae about thirteen ; the first formed eight or nine are regular, 

 closely arranged, and concentrically or elliptically curved, narrow, high-ridged, and 

 imperfectly tuberculated ; the last formed four or five costae are more widely separated, 

 and are more nearly horizontal, excepting their posteal portions, which have the tubercles, 

 to the number of three or four, larger and more curved upwards, approaching the carina 

 at a considerable angle. 



Length 14 lines ; height 11 lines ; diameter through the single valve 4 lines. 



The general figure and ornamentation approaches to T. concentrica Ag., but the rows 

 of costae are much less regularly and less distinctly tuberculated, the last formed rows 

 more especially are very narrow, less moniliform, and more horizontal, excepting their 



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