90 BRITISH FOSSIL TRIGONIyE. 



ante-carinal space. Apparently this is the form figured by De Loriol and Pellat for tlie 

 T. variegata of Credner (' Monog. de la Portland, de Boulogne,' 1865, pi. 7, figs. 6, 7) ; 

 the latter species, which is from the Kimmeridge strata of Fritzow, has large oblong nodes 

 upon the posteal portions of the costse ; these are much fewer, and the ante-carinal space 

 is much smaller than in our variety. In the expectation that examples of T. variegata 

 might occur in the Portland formation of England I have attentively examined a multi- 

 tude of examples of the Glabra from its beds, but have failed to ascertain its presence ; 

 perhaps, considering the general very limited stratigraphical range of the Trigovice, we 

 should scarcely expect to discover one of its Kimmeridge Clay species in the Portland 

 Oolite ; our British examples from the upper and lower stages of the formation indicate 

 this distinctness very conclusively. The figures in the little work of Credner (' Ueber die 

 Gliederung der Obern Juraformation und der Weaklen Bildung in Nordwestlichen 

 Deutschland, &c.,' Prag, 1863) are, upon the whole, coarsely engraved, and the drawings 

 of the Tngonice are apparently not very reliable for correctness ; in them we observe only 

 a remote resemblance to the two figures of T. variegata given by De Loriol and Pellat from 

 Boulogne. 



Por the most part the size and general aspect of the ante-carinal space affords a good 

 distinctive feature for the Glabra, and aids materially in the separation of its species, but 

 in the present, as in some other instances, it assumes an amount of variability indicative 

 of its subordination to some other specific characters. Other variable examples of this 

 feature are seen in the smooth or typical form of T. gibbosa, in which the space is smaller 

 and less distinct than in the other varieties ; the same remark will also apply to certain 

 examples of T. Juddiana and of T. irregularis in the Clavellatce and to 1\ angulata in the 

 Undulata j but it is only in the Glabra that this feature, from its constancy and promi- 

 nence, becomes of sectional importance. 



Trigonia tenuitexta, Lijcett, sp. nov. Plate XX, figs. 1, 1 «. 



Shell with the general outHne of T. Damoniana, but with less convexity ; the most 

 striking pecuHarity is afforded by the ante-carinal space, which is nearly absent ; there is 

 only a narrow slight depression indicating its position ; the knotted costse upon the side 

 of the valve are remarkable for their minuteness, close arrangement, and irregularity or 

 undulations, so that they appear partially confused ; they are also continued more or less 

 obscurely even across the ante-carinal space ; upon the umbonal portion the minute tu- 

 bercles with which the costse are crowded, disappear, and they there form a very numerous, 

 minute, plain, or almost hnear series. Upon the specimen figured the escutcheon has a 

 few regular oblique plications ; as this feature is one altogether foreign to the Glabra, and 

 occurs only in the Quadrata, the Scabra, and the Costata, its occurrence in the present 

 instance may be regarded as only an abnormal or individual peculiarity. 



