UNDULATiE. 55 



nodulous, and the larger or posteal costge disappear in their course upwards, leaving a 

 smooth, plain, and depressed space separating them from the carina. 



The first of the two figures of T. unddata, From., given by Agassiz (' Trigonies,' pi. 6, 

 fig. 1), has been quoted by D'Orbigny and by Oppel as a synonym of T. angulata ; in 

 this opinion I cannot concur, the large varices upon the marginal and inner carinae, together 

 with the considerable breadth of the area, appear clearly to separate the Swiss Great 

 Oolite fossil. The second example of T. undidata ('Trigonies,' pi. 10, fig. 14) is another 

 equally distinct species, and still more removed from T. angulata. 



The authors above quoted appear to have had little confidence in the figure of 

 T. angidata given in the ' Mineral Conchology/ which, although rudely engraved, is really 

 a good drawing and faithfully renders the characters of the species in a small specimen. 



T. an(julata has more or less affinities with all the species of the Undulates : for 

 distinctive differences the reader is referred to the descriptions of the numerous forms 

 depicted upon Plates X to XVI inclusive. 



Stratigra/plncal position and Localities. T. angulata has occurred in the Inferior Oolite 

 of Nunney, near Frome, whence the type-specimen, associated with Astarte elegans, 

 was obtained ; Dundry, in the same county, is another locality. I have obtained it at 

 various Gloucestershire localities in the Oolite-marl and in the Upper Grit-stones of the 

 same formation in the Cotteswold Hills, but the entire number of examples which have 

 come under my notice are inconsiderable, and no evidence has been obtained connecting 

 the species with the southern portion of Somersetshire, or of Dorsetshire ; it also appears 

 to be absent throughout the long coarse of the Inferior Oolite in Oxfordshire, Northamp- 

 tonshire, Bedfordshire, Lincolnshire, and Yorkshire. Upon the whole, therefore, it may 

 be regarded as a rare species. 



In France T. angulata has been described by Oppel (' Juraformation,' p. 485) as a 

 species of the Cornbrash at Marquise, near Boulogne ; some fine specimens from that 

 formation and locality attributed to our species have been found upon examination to be 

 T. flecta. D'Orbigny ('Prodrome,' 1, p. 308) places our species in his Etage 11, 

 Bathonien. Roemer (' Nordd. Oolith.,' p. 96) records the occurrence of T. angulata in the 

 Dogger of Porta Westphalica. 



Trigonia flecta, Mor. and Lgc. Plate XIV, figs. 7, 8, 9, 10. 



Tbigonia angulata, VOrhigny. Prodrome de Paleont., 1850, vol. i, p. 308. 



— PLECTA, Mor. and Lijc. Monogr. Gr. Ool., Pal. Sec, 18.53, p. 60, pi, v, 



fig. 20. 



— — Morris. Catal., 1854, p. 228. 



— ANGULATA, Oppel. Juraformation, 1857, p. 485, No. 45. 



Shell sub-ovate, or ovately oblong, somewhat depressed; umbones antero-mesial, 



