248 Mr. J. Lycett on some new species 0/ Trigonia 



species of Trigonia, it will be found that about two-thirds arc 

 proper to the Oolitic rocks ; and although some little abatement 

 must be made, for instances in which young individuals, varieties, 

 or mere casts have been erected into distinct species, the predo- 

 minance of Oolitic forms will remain, inasmuch as the Cretaceous 

 species are not exempt from similar errors of augmentation. 

 The inadequate manner in which the Inferior Oolite Trigonia 

 have been illustrated, will appear, when it is stated that of the 

 sixteen species recorded in the present paper, four only will be 

 found illustrated in the range of English literature ; a fifth occurs 

 in the ' Me*moire sur les Trigonees ' of Agassiz, and two others 

 are on the eve of being published in a * Monograph of the 

 Palseontographical Society/ leaving upwards of nine species un- 

 figured, a number which will be admitted to be remarkable when 

 we remember that M. D'Orbigny has only enumerated seven in 

 his ' Prodrome de Paleontologie ' for the Terrain Bajocien of the 

 whole of France, and M. Agassiz twelve from the entire lower 

 Oolite rocks of Germany, France and Switzerland. The present 

 examination of Inferior Oolite species has been suggested by the 

 frequent occurrence in collections of Trigonia cost at a, clavellata 

 and angulata, or of shells bearing those names, pertaining to 

 nearly the entire series of the Oolitic rocks of England and 

 France ; the aspect of these shells is so varied and dissimilar, 

 that they agree with each other and with the typical forms of 

 those species only, inasmuch as the first portion is costated, the 

 second clavellated, and the remainder have their costse bent to 

 form an angle. 



M. Agassiz, in his valuable memoir on Trigonia , arranged the 

 species into upwards of eight sections, some of which appear to 

 be separated by distinctions so transitive that it is scarcely pos- 

 sible to apply them to a large number of specimens, except in 

 an arbitrary and unsatisfactory manner ; a more simple arrange- 

 ment here proposed will probably answer every practical purpose, 

 and has at least the advantage of being more readily understood 

 and applied ; the genus will thus form six sections, of which one, 

 the Pectines, is recent only ; the five fossil sections consisting of 

 the Costatae, the Clavellatae, the Quadratse, the Scabrse, and the 

 Glabra?. The Costata have a figure more arched than the other 

 sectional forms ; they have smooth regular longitudinal ribs, 

 which are separated from the posterior slope or area by a carina 

 more or less prominent, but which, with advance of age, often 

 becomes nearly obliterated ; this is the marginal carina ; the area 

 has transverse striations which are frequently decussated by lon- 

 gitudinal plications, and by one or two, more prominent than the 

 othei-3, that which bounds the area posteriorly being the inner 

 carina ; should a third carina be present between the two others, 



