36 



BRITISH FOSSIL TRIGONLE. 



the umbo to the lower extremity of the shell ; the less conspicuous umbones, and great 

 comparative breadth of the area, are also so remarkable that they impart a sub-quadrate 

 aspect to the whole, and a wide truncation to the posterior side ; the fringing tubercles 

 of the costse are also more dense and delicate than in T. formosa. Length of an adult 

 specimen of T. formosa 29 lines ; height 24 lines. 



Stratigraphical position and localities. T. formosa has occurred in the Inferior 

 Oolite at Dundry Hill, but probably not at any more southward locality in Somersetshire 

 or Dorsetshire, where it is replaced by T. striata. In the Cotteswold Hills it has 

 occurred in the Supra-liassic Sands at Frocester Hill, and also in several beds in the 

 Inferior Oolite, beneath the upper Trigonia Grit, at various localities, more especially at 

 Cold Comfort, near Cheltenham, and at Rodborough Hill, near Stroud ; it appears to be 

 altogether absent in the Inferior Oolite, in its extension through the counties of Oxford, 

 Northampton, Lincoln, and York. Another and nearly allied species from the red Inferior 

 Oolite of Moutiers, Normandy, has the general figure and orna- 

 mentation nearly resembling T. formosa, excepting that the 

 Moutiers form has greater convexity, and the escutcheon has 

 greater breadth ; the rows of costse increase in size anteally, and 

 the tubercles have each a small pillar, which descends perpendi- 

 cularly to the costse next in succession. The space between the 

 anteal extremities of the costae and the border has a numerous series 

 of small transverse supplementary costae. All the examples which 

 have come under my notice are smaller than average specimens of 

 T. striata or T. formosa. The British Museum has a fine series. 

 I propose for it the name Trigonia Moutierensis. 



Trigonia striata, Miller. Plate V, figs. G', 7, 8. 



Trigonia striata, Sow. Min. Choi., 1819, t. 237, figs. 1, 2. 

 _ _ Morris. Catal., 1854, p. 229. 



— — Oppel. Juraformation, 1857, p. 407. 



Shell subquadrate, short, moderately convex; umbones small, erect, only slightly 

 recurved, antero-mesial ; anterior side short, somewhat truncated, lower border curved 

 elliptically ; superior border short, horizontal, forming a considerable angle with the wide 

 truncated extremity of the area ; the length of this truncated border exceeds that of the 

 superior border. Area very wide and flattened, traversed mesially by an obscure furrow 

 which slightly bends the transverse striations ; these are very regular and minute, even to 

 the apex. There is no mesial carina, and almost no inner carina, as the transverse 



