8 BRITISH FOSSIL TRIGONI^E. 



varieties of Trigonia signata^ which are herewith figured, and named as varieties, and 

 described. These, it will be observed, occur only at a lower position in the Inferior 

 Oolite, apparently in the zone of Ammonites MurcJiisoni ; they seem not to be known 

 beyond the limits of Oxfordshire, unless possibly the variety rugulosa may be identical 

 with the figure of T. elavellaia, Quenstedt, 'Jura,' tab. 60, fig. 13, from the Brown Jura 

 of Swabia. 



At page 221 are remarks upon the abundance and variety of the Clavellat^e in the 

 Middle and Upper Jurassic Rocks, and of their sudden disappearance thereafter. We 

 might naturally expect to find the progenitors of these forms, so numerous and varied, in 

 some of the older beds containing Trigonise ; it is my present belief and impression that 

 in the Inferior Oolite of Oxfordshire we have the precursors of at least two of the more 

 abundant of the later forms, and that the variety under notice should be placed 

 zoologically as an analogue of T. ingens of the Neocomian Rocks. 



Trigonia signata, Ag., var. rugulosa, Lycett. Trigon. Supplement, Plate II, figs. 1, 

 2, 3 ; Plate IV, figs. 2, 4. 



Dimensions equal to the more common variety 1\ signata, var. Zietenii, but the test 

 is thicker and more ponderous ; the convexity is more considerable, the area narrow, steep, 

 and slightly expanded, the hinge-border is comparatively short and depressed, the 

 siphonal border obhque, forming only a small angle with the hinge-border; the lower 

 termination of the siphonal border is produced and pointed; the area altogether is 

 extremely rugose, especially its bounding carina3 ; its transverse costellae, where they are 

 distinct, form a double curvature when well defined, and are depressed in the middle by 

 the median furrow ; the lower third of the area has the plications large, oblique, rugose, and 

 irregular. The rows of costae (about 1 5) are large with much upward curvature posteriorly, 

 the tubercles in the rows are for the most part closely placed and are larger than in var. 

 Zietenii ; they become partially cord-like, but are large and very unequal even to the 

 pallial border ; the first-formed two or three rows of costas are quite plain, as in the 

 other varieties. The rugose aspect of the whole shell is very striking and remarkable. 



An unusually fine specimen with the valves open, now in the Geological Survey 

 Museum, London, exhibits the peculiarities of this variety in a very conspicuous manner ; 

 it was worked out by myself about thirty years ago, and was known to have been obtained 

 in the vicinity of Chipping Norton. It is alluded to in the IMonograph, page 30, and 

 would have been figured had not its geological position at that time remained doubtful ; 

 it is, indeed, only very recently that the exact position of this variety has become known, 

 the three specimens herewith figured, Plate II, figs. 1, 2, 3, collected by Mr. Walford 

 and Mr. Windoes, and the two by Mr. Stutterd, Plate IV, figs. 2, 4, amply illustrate 



