BRITISH FOSSIL TRIGONLE. 



Trigonia Oviedensis, Lycett. Sp. nov. Woodcuts, figs. 1 and 2, nat, size. 



Shell ovately oblong, somewhat Unio-like, moderately convex anteally and mesially, 

 more depressed posteriorly ; umbones not very large or prominent, but pointed, and 

 situated within the anterior third of the valve ; the ornamented or costated portion of 

 the surface occupies about three-fourths of the valve ; the costse are very numerous, very 

 closely arranged, not prominent, for the most part closely and imperfectly tuberculated ; 

 the tubercles are depressed and often obscure ; the general direction of the rows is 

 horizontal, those occupying the first four lines in height adjacent to the apex are linear 

 and nearly smooth ; their arrangement is so close that about twenty-five may be 

 counted ; the costae of the other and greater portion of the valve, about twenty-five in 

 number, are tuberculated and horizontal ; the rows become somewhat more prominent at 



Fig. 1. 



Fig. 2. 



Trigonia Oviedensis, from Spain. 



their posteal extremities, where they terminate abruptly at the smooth ante-carinal 

 space ; they are sometimes undulated, but all have a general horizontal direction. The 

 smaller or smooth portion of the shell, represents a narrow ante-carinal space, a narrow 

 smooth area with obscure bounding carinse, and a narrow, lengthened escutcheon ; the 

 latter is about half the length of the entire valve ; the area has also a slightly defined 

 mesial furrow. The specimens contributed by Dr. Barrois differ among themselves in the 

 prominence of the subtuberculated costse, but the general figure of the shell is nearly 

 alike though essentially different from its allied congeners of the glabra, from which it 

 it is separated by the ovately oblong figure, by the small umbones and by their 

 anteal position. 



In the character of the ornamentation in T. Oviedensis there is a remarkable fact, 

 inasmuch as it is nearly allied to a species of the same section (Glabra) placed almost 

 at the opposite extremity of the Jurassic species, viz. the T. tenuitexla, Lye, of the 

 Portland formation j 1 but in the general figure the two species are strikingly different ; 

 in fact the shape is the feature by which T. Oviedensis is most conspicuously distin- 

 guished, and which at once separates it from the Portlandian Glabra. 



1 Monograph, p. 90. 



