233 Mr. J. Lycett on some neiv species o/Trigonia 



serrated. The truncation at the posterior extremity is so consi- 

 derable that the breadth of the area at that part is equal to half 

 the entire length of the shell, or to three-fifths of the height ; 

 the length of the marginal carina is 20 lines. 



The upper portion of the middle division of the Inferior Oolite 

 has furnished the few specimens which have been procured ; the 

 locality is Scar Hill near Nailsworth. 



Trigonia exigua, Lycett, n. sp. PI. XI. fig. 3. 



Shell small, subtrigonal, depressed ; umbones mesial, not re- 

 curved, anterior border nearly straight, oblique, posterior border 

 truncated ; area moderately large, flattened, transversely ribbed, 

 and having an obscure oblique mesial furrow, no distinct carinse, 

 the marginal carina being replaced by a series of small nodulous 

 elevations upon the posterior extremities of the costse. Costse 

 smooth, cm-ved, closely arranged, rounded, and slightly bent 

 upwards as they approach the area, their number being about 

 fourteen. 



The costEe upon the area are smaller and rather more nume- 

 rous, for an intercalated rib is sometimes added. Specimens 

 vary from 2 to 5 lines in length, the latter dimensions seeming 

 to represent the adult form. 



From T. costatula it is distinguished by the much smaller 

 dimensions and by the absence of any distinct marginal carina, 

 the costse being continued over its position upon the area. 



Trigonia concinna, Rcemer, Nord. Ool. Nachtrag. p. 35. tab. 19. 

 fig. 21. approximates to our shell in the general figure and dis- 

 position of the costse, but his shell would appear to have greater 

 convexity and a larger area, and the costse upon the area appear 

 to be as large as those upon the other portion of the surface ; it 

 is therefore probably a distinct species. 



Our little shell occurs not uncommonly in the shelly freestone 

 of Leckhampton Hill ; it has also occurred in the same beds near 

 to Nailsworth. 



Trigonia v.-costata, Lycett. PI. XL fig. 7. 

 Trigonia v.-costata, Lycett in Ann. & Mag. Nat. Hist. 1850, p. 422. 

 Shell ovately trigonal, moderately convex, anterior and infe- 

 rior margins- rounded, posterior margin straight or slightly con- 

 cave ; umbones obtuse, slightly recurved ; area narrow, flattened, 

 its upper portion transversely plicated, its lower portion nearly 

 smooth, divided in its middle by an obliquely longitudinal fur- 

 row ; marginal and inner carinse but faintly marked and striated, 

 the inner carina being crossed by several varices. The costse are 

 very numerous, smooth and regular, they are directed from the 



