133 



posteally, hinge-border lengthened concave, terminating posteally 

 in a rostrated and attenuated extremity, ligamental aperture 

 narrow, inter-umbonal ; escutcheon lengthened, deeply concave, 

 occupying the entire upper surface of the shell, its superior or 

 inner border is plain and much raised ; its outer border is 

 elevated and rounded ; the area is very narrow and convex ; it is 

 rendered bipartite throughout its entire length by a deep groove, 

 and its superior or umbonal portion has a few small, ridge-like 

 transverse costellse; the remainder of its length has small, 

 irregular, transverse, plications. The other portion of the surface 

 has a numerous series of costee which originate at the border of 

 the area as narrow crenulated ridges, and diverge in every direc- 

 tion ; about seven costse nearest to the apex are concentric or 

 curved obliquely, the next succeeding seven become inflated at 

 their middle portions, and pass obliquely downwards to the 

 pallial border. The change from the inflated anteal surface to 

 the depressed and flattened posteal portion is abrupt, and is a 

 strong characteristic of the species. 



T. aliformis occurs in the Chloritic Sands of Chardstock. 



EXCLUDED SPECIES. 

 TEIGONIA BKONNII, Ag. 

 MONO. BEIT. FOBS., TRIOONLE, Lye., Pal. Soc.. p. 23, 209, plate iv., fig. 8. 



Professor Hebert, in his memoir on certain clavellated Trigonige 

 of the Oxford Clay and Coral Kag, refers to four British 

 specimens of T. Bronnii found in the Calcareous Grit of Wey- 

 mouth, which appeared to coincide with some French examples 

 of T. Bronnii, a species which has a considerable variability 

 even when obtained from a single locality, subsequent examina- 

 tion and comparisons of Weymouth and French specimens con- 

 vinced him of the fallible character of this single distinctive 

 feature and of the necessity of merging all such Weymouth 

 specimens in T. clavellata. 



The above descriptions are all taken from Dr. Lycett's Mono- 



