POSITIONS OF THE TKIGONIJE OF NOETH OXFORDSHIRE, ETC. 45 



TRiGOiSriA PiTLLUS, Sow. Stonosfleld Slate, Stonesfield, upper zone. 

 Great Oolite, near Banbury, and Forest Marble, near RoUright. 



A beautiful costate species from the upper zone of the Great Oolite 

 at Capps Lodge, near Burford, furnishes an instance of the difficulty 

 of finding names for the whole of the varied forms of the group. Mr. 

 W. H. Hudleston, F.R.S., F.G.S., has kindly allowed me to examine a 

 specimen more perfect than any in my own cabinet ; and from it 

 the following description has been written : — height If inch, width 

 1 J inch, breadth of area 1 inch, breadth of escutcheon | inch, depth 

 of unitedValves Ig inch. The breadth of the area is thus two thirds 

 that of the costated part of the shell. The umbones are pointed and 

 recurved. The anterior border is first curved and then slightly 

 straightened as it sweeps towards the lower border. The costse, 27 

 in number, are prominently elevated with sharp ridges and deep 

 interspaces, undulating slightly as they curve gently downwards 

 and then cross transversely towards the carina. The marginal 

 cariDa is greatly elevated, in the lower part of the shell as much as 

 -i inch above the costse ; it is also boldly denticulated. The area is 

 divided by a tuberculated median carina in the left valve, with a 

 corresponding groove in the right valve and a prominent adjacent row 

 of costellse. It is ornamented by four rows of costellse, which are 

 decussated by transverse markings. The escutcheon is ovately cor- 

 date and is bounded by prominent tuberculate or denticulate carinse. 

 It has a raised cushion-like centre and numerous longitudinal lines. 

 The area is concave. 



It differs from T. elongata in the want of convexity near the 

 carina, and also in its wider form ; the area, however, has much 

 similarity. The escutcheon is not that of the ordinary type of 

 T. puUus, and the area is larger. Though it seems to find a place 

 between the two species, it will suffice for the present to look upon 

 it as a variety of T. pullus. 



Trigonia Painei, Lye, is found in the Great Oolite of Groves 

 Quarry, Milton, near Burford, though it does not there exhibit the 

 massive ornamentation of the Inferior-Oolite and FuUer's-earth forms 

 previously mentioned p. 41. 



Trigonia, sp. — Height IJ inch, breadth 2 inches. Shell convex. 

 Umbo slightly recurved, antero-mesial. Surface covered with about 

 twenty bold slightly waved costae, which cross the shell with but a 

 slight curve toward the lower margin. The lower seven costse, when 

 about a third of their length distant from the carina, are crossed and 

 nearly obliterated by three bold rows of nodulous costae bearing 

 downwards almost vertically from the carina. The area takes up 

 about a third of the shell and is convex posteriorly. Anteriorly the 

 strong costse cross the area, but appear to pass into fewer striae in 

 the lower half of the shell. It is so much like the shell figured by 

 Morris and Lycett on tab. v. pt. ii. of their ' Monograph of the 

 Mollusca from the Great Oolite,' as T. Goldfussi (subsequently 

 altered to T. Painei), that for the present it seems best to let the 

 species pass with this reference. 



