12 BRITISH FOSSIL TRIGONI^E. 



Trigonia Moretoni, var. Oxoniensis, Lycett. Trigon. Supplement, Plate I, figs. 13 — 15. 



The typical or Great-Oolite variety of Trigonia Moretoni has been sufficiently 

 depicted in the Monograph on Plate II, figs. 4, 5, 7, 8, also Plate IV, fig. 6, and has 

 been described pp. 47, 59, 63, 70, 78 ; it is there shown to be a very variable species 

 even in the Great Oolite, and I have now to describe a distinct variety which has been 

 obtained rather sparingly by Mr. Walford and by Mr. Windoes in the lower beds of the 

 Inferior Oolite at Hook Norton, Oxon. 



All the specimens of Trigonia Moretoni, var. Oxoniensis, obtained are smaller than 

 the typical form, and differ from it in the following features : the entire ornamentation of 

 shell is larger and bolder or more strongly defined ; the concentric costae are fringed 

 with papillae, from the pallial margin to the apex; they are remarkably prominent, 

 regular, and concentric ; their papilla3 are also very large, rounded, and elevated ; but 

 even these costse are not without variability, for, notwithstanding this regularity, some 

 specimens have the costae rather transverse than concentric, with little curvature. The 

 area has its costellae unusually elevated, and scarcely any two specimens have them alike ; 

 but the inner carina is always distinct, prominent, and spinosc. The largest shells of 

 this little variety are not more than six lines across the valve. 



It may be a matter of doubt whether I am justified in placing this little species as a 

 variety of T. Moretoni, it differs so considerably from the Great-Oolite forms ; the limits 

 of variability assumed by this species are in truth so considerable that I feel much 

 diffidence in deciding upon differences with strata having a wide stratigraphical separation. 

 Apparently the present specimens are not of adult growth, and the decision of this question 

 may be relegated to a period when the number of known specimens shall have become 

 more considerable, and the results of comparison more certain. 



Trigonia Formosa, Lycett. Trigon. Monogr., Plate V, figs. 4, 5, 6 ; Plate XI, fig. 2 ; 



Plate XXXVII, fig. 10; var /«/«, Plate XXIX, figs. 11, 

 12 ; var. lata, PI. XXXV, fig. 7 ; Trigon. Supplement, 

 Plate I, figs. 11, 12. 



I am induced to figure the tw^o forms on Plate II, figs. 11 and 12, on account of the 

 great concavity of the area and hinge-border : of these the Rev. Mr. Wiltshire has also sent 

 me other fine specimens. The contrast afforded by these forms when compared with the 

 Trigonia striata of Dorsetshire and Somersetshire is very striking, and fully justifies the 

 separation I have made between that species and the T.formosa of the Cotteswolds. I 

 do not, however, altogether perceive the necessity of erecting the present into a distinct 



