238 Mr. J. Lycett on some new species o/Trigonia 



Trigonia angulata, Sow. 



Trigonia angulata, Sow. Min. Con. tab. 508. fig. 1. 



Trigonia clavellata, Sow. Min. Con. tab. 87j the two lower figures. 



Shell elongated and rostrated, posterior border concave, ante- 

 rior border rounded ; umboues recurved ; area narrow, bounded 

 by small crenated carinse; costse narrow, closely arranged, 

 straight anteriorly, undulated posteriorly, where they forai large 

 tuberculated varices, the few last varices directed downwards. 

 M. D'Orbigny (Prodrome de Paleontologie) considers Trigonia 

 undulata^ Fromberg, to be only a synonym of T. angulata : in this 

 opinion I do not concur ; the figure of the two shells is essentially 

 different, T. angulata being much more elongated, and the um- 

 bones more recurved; the surface ornaments of the shells like- 

 wise differ; those of T. angulata are remarkably constant and 

 invariable. 



T. undulata has not been recognized in the Oolites of England ; 

 on the other hand, T. angulata has not been discovered upon the 

 continent. T. angulata has occurred at many localities in the 

 Cotteswolds, both in the middle and upper portions of the Infe- 

 rior Oolite, but it is rare. The imperfect specimen of T. angu- 

 lata from Little Sodbury, which is given in the two lower figures 

 of table 87 of the ' Mineral Conchology ' as T. clavellata, has 

 been the source of much confusion to subsequent observers, and 

 has led them to catalogue clavellated specimens (usually imper- 

 fectly exposed) as Trigonia clavellata ; but the figure in the same 

 work of T. angulata is so characteristic, that it may be relied 

 upon when the shell itself cannot be obtained for comparison. 



Trigonia duplicata, Sow. 

 Trigonia duplicata^ Sow. Min. Con. tab. 237. figs. 4, 5. 



Shell slightly rostrated, area narrow, carinse two in each valve, 

 small, distinct ; costse narrow, serrated, the first few concentric, 

 the others directed downwards, for the most part bifurcated and 

 slightly waved. Should the T. Proserpina of D'Orbigny prove 

 to be distinct from this species, it must possess peculiarities 

 which are not alluded to in his ' Prodrome de Paleontologie,' 

 where the brief description given agrees with T. duplicata. M. 

 Agassiz (probably from an imperfect knowledge of the species) 

 has placed T. duplicata with the Scabrce, but the very distinct 

 marginal carina and the area destitute of transverse costse clearly 

 remove it from that section, which first appeared with the species 

 of the lower greensand. 



T. duplicata occurs in the upper division of the Inferior Oolite 

 in the Cotteswolds, where the external impressions are not un- 



