12 BRITISH FOSSIL TRIGONLE. 



history of the genus these few species exemplify three of the sections into which the 

 genus is divided. Three of these {1\ denticulata, T. spinulosa, and T. formosa) pass 

 upwards into the Inferior Oolite, in which they are more abundant. T. liamsayi, and T. 

 Leckenbyi are special to this stage. 



In Britain the Inferior Oolite appears to have been the very metropolis of the 

 Trigonise. Upwards of twenty-seven species have rewarded the industry of collectors ; from 

 its geographical position it forms four areas, severally from which the following species 

 have been obtained : 



] . Area to the southward of the Mendip Hills, including the counties of Somerset and Dorset. 

 T. costata, T. striata, T. formosa, T. duplicata, T. angulata, T. tenuicosta, T. signata. 



2. Area of the Cotteswold Hills. 



T. costata, T. sculpta, T. denticulata, T. hemispharica, T. costatula, T. angulata, T. 

 sub-globosa, T. producta, T. signata, T. Phillipsi, T. V-costata, T. pulla, T. tuberculosa, 

 T. formosa, T. duplicata, T. gemmata, T. spinulosa, T. tenuicosta. 



3. Area of the Midland Counties and Lincoln. 



T. sculpta, T. denticulata, T. gregarea, T. hemisphcerica, T. pulla, T. formosa, T. 

 signata, T. Phillipsi, T. V-costata, T. Sharpiana, T. compta, T. minor, T. Beesleyana, 

 T. producta. 



4. Area of Yorkshire. 



T. denticulata, T. gregarea, T. conjungens, T. spinulosa, T. V-costata, T. recticosta, 

 T. signata. 



Prom the foregoing lists it will be perceived that the areas of the Cotteswold Hills 

 and of the Midland Counties have many species in common, but that the Somerset and 

 Dorset area and that of Yorkshire have only a single species identical. Of these twenty- 

 seven species two only {T. denticulata and T. pulla) have been found to pass into a higher 

 formation. 



The Bathonian formation has also a greatly varied but less numerous series, seventeen 

 in number, as follows : 



T. pulla, T. denticulata, T. Bathonica, T. arata, T. Moretoni, T. impressa, T. Painei, 

 T. Crucis, T. Griesbachi, T. jiecta, T. Clytia, T. imbricata ; also the following, which 

 appear to be special to the Cornbrash : T. Scarburgensis, T. Cassiope, T. tripartita, T. 

 angustata, T. bivirgata. Of these I have been able to trace only T. denticulata into a higher 

 formation. 



