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BRITISH FOSSIL TRIGONLE. 



outline of the shell is less orbicular, or is more lengthened in the direction of the 

 divisional angle of the valve. The moulds have the costae less conspicuous ; their edges 

 are almost smooth, having only slight indications of the obtuse spines which ornament 

 the test. Upon the whole this variety from the Upper Greensand is readily recognised 

 when compared with the typical form from the Blackdown Greensand ; the more 

 lengthened form appears to require a varietal designation (subovata), as it is readily 

 recognised irrespective of the lesser differences alluded to. 



Trigonia Formosa, Lye, var. lata. Page 35, PI. XXIX, figs. 11, 12 ; PI. XXXV, 



fig. 7. 



The specimens of T. formosa figured PI. V, figs. 4 — 6, also PI. XI, fig. 2, and 

 an additional specimen, PI. XXXVII, fig. 10, are characteristic forms of the species 

 as it occurs in the Cotteswold Hills. In Somersetshire a shell occurs, recognised 

 generally as T. formosa, which I regard as a variety {lata) of the Cotteswold form ; these 

 examples are figured, PI. XXIX, figs. 11,12; and PI. XXXV, fig. 7. 



Compared with the Cotteswold or typical form, the shell has somewhat less convexity, 

 more especially upon the anal portion, which is more flattened and expanded ; the area 

 has greater breadth ; the siphonal border is more lengthened and oblique, forming a 

 smaller angle with the escutcheon, which is shorter and more horizontal ; the transverse 

 striations, which are small and regular in the Cotteswold form, become larger and fewer 

 near to the apex in the variety ; the costae are variable in the specimens examined, but 

 do not present any clear distinction. 



At Bradford Abbas this variety is not uncommon ; it occurs also at Haselbury, 

 Somerset, accompanied by Trigonia costata and by the Conchifera usually met with at 

 the former locality, but the state of preservation is much inferior. At Milcomb Hill, 

 Oxon., it has been recorded by Mr. Beesley in the Northampton Sands. 



Trigonia Archiaciana, D'Orb. Page 140, PI. XXIII, fig. 7. 



In reference to this species I have been favoured with the following remarks by 

 Mr. C. J. A. Meyer, whose researches in connection with associated species of the 

 Upper Greensands and Chloritic Marls of the southern counties of England entitle his 

 opinions to the highest consideration. I fully agree with the following conclusions : 



" It appears likely that two or three nearly allied species have long been included 

 under the name of Archiaciana on account of the great similarity of their surface 

 markings and the unusually indifferent condition of the specimens examined. And 

 supposing that there are three species which have been included under the one name, the 

 following might, I think, be a safe provisional arrangement : 



