﻿COSTATtE. 



151 



Pusch, ' Polens Palaontologie,' p. 58, tab. 7, figs. 1, 2, described and figured, as a 

 variety of T. costata, a remarkable example of the section in which, as also in the 

 glabrce, a diagonal space exists, anterior to the marginal carina, entirely devoid of 

 ornamentation; this species was separated by Agassiz under the name of T. zonata 

 ('Trigon.,' p. 36), and by Quenstedt as T. interlavigata (' Der Jura,' p. 503, tab. lxvii, 

 fig. 8). Oppel also described it under the latter name (' Juraformation, p. 486, No. 49). 

 Apparently it pertains to the horizon of the Cornbrash at Ehningen, Oeschingen, also 

 near Freiburg. 



A shell figured by Goldfuss under the name of T. costata, var. triangularis 

 (' Petrefacten.,' t. cxxxvii, fig. 3 d), is evidently nearly allied to T. zonata, but is apparently 

 distinct. The outline presents some differences in the greater height and shortness, and 

 in the greater elevation of the escutcheon ; other distinctions consist in the delicate 

 costellse upon the area, the small carinas, and the more numerous and delicate costse ; it 

 is from the Black Limestone of Liibke, the geological position of which I am unable 

 to correlate ; both of these forms are unknown in British strata. 



The T. costata of Chapuis and Dewalque ('Foss. Ter. Second, de Luxembourg,' 

 p. 170, pi. 25, fig. 8) represents an elegant species, which differs not only from 

 T. costata, but also from every other example of the section known to me ; it is remarkable 

 for the great extent to which the anterior side is produced, so that the recurved apices 

 of the valves are placed a little posterior to a line drawn perpendicularly through the 

 middle of the shell ; the escutcheon is remarkably large and transversely minutely 

 costulated ; the ligamental fossa is unusually lengthened ; the area is very narrow, with 

 a minutely reticulated surface, which is represented as alike upon both the valves ; the 

 bounding carinas are small, and accord with the other delicate features of the area ; the 

 siphonal border is unusually short : altogether, the drawing differs so materially from 

 the description given in the text as to lead to the con- 

 clusion that the latter was founded upon true examples 

 of T. costata, and that by some error another costated 

 form was substituted in the plate for the species in- 

 tended to be represented. 



Another interesting allied species, derived almost 

 from our antipodes, is T. Moorei, Lyc. (Moore's memoir 

 on "Australian Mesozoic Geology," ' Quart. Journ. Geol. 

 Soc.,' vol. xxvi, p. 254, pi. 14, figs. 9, 10). Allied in 

 its general aspect to T. costata, it differs in having the 

 general figure more depressed ; the escutcheon is un- 



00 1 Trirjonia Moorei, Lyc. Western Australia. 



usually narrow and lengthened; the area is larger, 



more convex, and more expanded ; it is distinctly bipartite, but has no median carina ; 

 the inner carina is slightly nodular and inconspicuous. The costas are short and curved 

 concentrically ; anteally they approach the border almost perpendicularly ; there is no 



