42 



On Trichites, a fossil yenus of Bivalve Mollusks. 

 By John Lycett, Esq. 



Read 22nd January 1850, 



This generic form is distributed over an extensive area both in 

 this country and upon the continent; it occurs in more than one 

 of the oolitic formations; the Cotteswold Hills more especially 

 produce it abundantly ; nevertheless it is almost entirely absent 

 from the cabinets of English collectors ; and if we examine that 

 section of modern literature which professes to illustrate fossil 

 conchology, our search will scarcely be more successful or satis- 

 factory. In both cases the defect may be accounted for by a dif- 

 ficulty almost insurmountable experienced in obtaining illustra- 

 tive specimens in a condition perfect, or even approaching to 

 perfect ; fragments indeed are easily detached, but these alone do 

 not convey any precise or adequate idea of the generic characters. 

 The shells are large, the very Titans of their period, sometimes 

 extending to upwards of a yard across, of a thickness far sur- 

 passing that of bivalves generally, but of a structure peculiarly fra- 

 gile (prismatic crystalline), consisting of fibres closely arranged, 

 placed perpendicularly to the surface and breaking readily in the 

 direction of the fibres with any slight concussion ; this is a serious 

 obstacle to their separation, to which may be added, that the up- 

 per ragstone bed of the Inferior Oolite in which they most com- 

 monly occur is very hard and intractable in the nature of its 

 fracture. In almost every open quarry of this rock, and more 

 especially in the stratum called Trigonia grit, these thick fibrous 

 masses may be noticed ; more rarely also in the middle portion 

 of the same formation and in the shelly beds of the Great Oolite. 

 They have usually been referred to a gigantic species of Pinna, 

 probably from a similarity of structure. The Cotteswolds have 

 produced two species, which are distinct from another recorded 

 from the Jura which will subsequently be noticed. Dr. Plott, 

 the historian of Oxfordshire, appears to have been the first per- 

 son who applied the term Trichites to these shells. Woodward, 

 in his ' Catalogue of English Fossils/ 1725, part 2. p. 101, 102, 

 ' De testis aliisque incerti generis/ mentions that Lhwyd sent a 

 specimen of this genus from the Oolite of Bullington Green near 

 Oxford, with the title " Trichites Plottii, Hist. Oxon. Veneris crincs 

 forean IMinio/' and adds the caustic remark, that these two writers, 

 Dr. Plott of mere simplicity, and Lhwyd of design, " darken 



