16 BRITISH FOSSIL TRIGONLE. 



T. gemmata is also allied to Lyrodon sulcatum, Goldf., from the White Chalk of Havre ; 

 but in that species the concentric costae occupy the whole of the anterior border. 



Stratigraphical position and localities. The bed called Upper Trigonia-grit of the 

 Inferior Oolite in the vicinity of Stroud and of Cheltenham j it appears to be one of the 

 most rare productions of that stratum. 



Trigonia recticosta, Lycett, sp. nov. Plate I, figs. 4, 5, 6. 



Shell ovately trigonal, moderately convex ; umbones small, antero-mesial, scarcely 

 recurved ; anterior side short, truncated, its border slightly curved, lower border nearly 

 straight; hinge-border straight, sloping obliquely downwards ; area flattened, very wide, 

 its breadth is equal to two fifths the entire breadth of the valve; it has a mesial furrow, 

 is transversely irregularly plicated, and is bounded by two small tuberculated carinas ; the 

 tubercles upon the marginal carina are regular, and nearly equal in size to those upon the 

 side costae ; the inner carina consists of a row of minute, unequal, transverse, nodose varices. 

 The costae, nineteen or twenty in number, are moderately elevated, with regular, small, 

 rounded tubercles ; the first-formed eight or nine rows are slightly curved or oblique, and 

 are directed towards the anterior border, where they are united to a series of short, ridge- 

 like, narrow, sub-tuberculated, horizontal costae, of which about nine occupy the anteal 

 portion of the valve ; the other costae pass almost perpendicularly to the pallial border, 

 increasing in size downwards without division or supplementary costae ; about twelve 

 tubercles are in each row. The lines of growth are strongly defined ; they form plications 

 where they cross the perpendicular costae. The general figure of the shell and the 

 direction of the rows of costae resemble T. duplicafa, but the costae are but little elevated 

 or ridge-like ; and, unlike that species, the tubercles are regular and symmetrical, the rows 

 are more distantly arranged, and are not divided near to the pallial border into several 

 smaller costae. 



Prom T. gemmata, the second of this group of Lower Oolite forms, it differs both in 

 its figure and in the arrangement of the costae, which are much fewer and more perpen- 

 dicular, with wide interstitial spaces, and it has not the numerous first-formed large 

 concentric rows of that species. It is also not without some general resemblance to a 

 young Trigonia navis, both in its figure and the design of its ornamentation; for dis- 

 tinctive difference it is only necessary to refer to the numerous costae and their minute 

 tubercles in the British species. 



Stratigraphical position and locality. The Inferior Oolite at Cloughton cliffs, to the 

 northward of Scarborough. The Millepore bed (so called from the prevalence of Cricopora 

 straminea) is there somewhat ferruginous ; it has produced a few well-preserved specimens 

 of our little Trigonia, and numerous others in an imperfect condition associated with 



