10 BRITISH POSSIL TRIGONIyE. 



liarity of their posteal attenuation and upward curvature, forming varices towards the 

 carina, would of itself be always sufficient to separate the two forms ; nevertheless, the 

 approximation is such that I think we may fairly regard this variety as the precursor of 

 the well-known species of the Middle Oolites. 



The remarkably fine example of this variety contributed by Mr. Stutterd, of Banbury, 

 and two others from my cabinet, constitute the three specimens on Plate IV. A 

 comparison of these, and of a fourth specimen sent by Mr. Stutterd, but not figured, as 

 well as a fifth in my cabinet, and of the three specimens from the collections of Mr. 

 Walford and Mr. Windoes figured on Plate II, figs, 1, 2, 3, — a comparison of these with 

 the figure of Tngonia trigona (Waagen, * Beitrage, iiber der Zone des Am. Sowerbyi,' 

 plate xxix, fig. 3, a, b) induces me to regard the species from Southern Germany as 

 constituting another variety of Tngonia signafa allied to the present Oxfordshire variety, 

 but distinct from all known British forms. 



The terminal posteal varix in each row of costse in our variety has a considerable 

 resemblance to Dr. Waagen's fine Trigonia, of which it constitutes a prominent feature 

 in the ornamentation ; the figure of the shell, however, and of surface ornaments 

 constitutes a distinction. 



Position and localities. — The specimens contributed by Mr. Stutterd (PI. IV, figs. 

 1, 5, 6) are from the Inferior Oolite of Rollright Heath; those on Plate II, figs. 1, 2, 3, 

 are from the Inferior Oolite of the Cross roads, near Over Norton. It is rare and 

 appears to be one of the most variable of the Oxfordshire forms in its general aspect and 

 ornaments. 



Trigonia signata, y«r. decurtata, Zyc<?^/. Trigon. Supplement, Plate I, figs. 1, 2; 



Plate IV, fig. 3. 



Shell with the general figure of T. signata, but less depressed and somewhat shorter 

 posteally ; umbones large and moderately recurved ; hinge-border somewhat concave, 

 sloping obliquely ; area of moderate breadth, somewhat raised and flattened ; transversely, 

 closely, and minutely striated throughout its entire length ; median carina very minutely 

 papillated ; the two bounding carina nearly similar in character, and not very distinctly 

 separable from the transverse striations. The other portion of the shell has curved rows 

 of costa3, which are less numerous than in the first two varieties, and are more irregular 

 in their general direction and aspect. 



Our description is founded upon two specimens which vary moderately from each 

 other in the characters of their pallial costae. In both specimens the first few rows are 

 sub-concentric or transverse, and minutely tuberculated, and become attenuated as they 

 approach the anterior border. The succeeding rows are for the most part obliquely 

 curved, but with less regularity; the tubercles are small, unequal, and sometimes 



