78 CRETACEOUS LAMELLIBRANCHIA. 



Trtgonia dunscombkxsis, Tiycett, 1877. Plate XIX, figs. 12 a, h. 



1877. Lijcpft, p. 188, pi. xl, figs. 5, 6 ; pi. xli, fig. 14. 



1896. A. J. Juices-Browne and W. Hill. Quart. Journ. Geol. Soc, vol. Hi, p. 153. 



Remarks. — Messrs. Jukes-Browne and Hill consider that T. dunscomhensis is 

 probably identical with T. siuufifa, d'Orbigny {lunt Parkinson) Avhich I regard 

 as a synonym of T. affinis (see p. 77). Small forms (;j-5 mm. long) seem to be 

 inseparable, unless it is by the somewhat greater convexity of T. dunscomhensis, 

 but the larger examples of the latter (e. r/. Lycett's fig. 5) seem to differ in having 

 a less ovoid outline and fewer ribs. More specimens of T. dunscombensis are 

 needed before its affinities can be definitely settled. 



Types. — Figs. 5 and 6, from near Sidmouth, are in Mr. Mej'er's collection. The 

 original of pi. xli, fig. 14, from Dunscombe, is in the Museum of Practical 

 Geology. 



Distrihiifion . — Cenomanian (Beds 10, 11, and 12 of Meyer) of Dunscombe, 

 Branscombe, Whitecliff, and Pinhay; Bed 11 of Humble Point, Lyme Regis. 

 Base of Chalk Marl (zone of Schloenbachia varians) of Titherleigh. 



Trigonia debilis, Lycett, 1877. 



1877. Lyrett, p. 189, pi. xl, fig. 8; pi. xli, fig. 5. 



1896. A. J. JnJces-Browne and W. Hill. Quart. Jouru. Geol. Soc, vol. lii, p. 154. 



Types. — In Mr. Meyer's collection (fig. 8), and in the Museum of Practical 

 Geology (fig. 5). 



Distribution. — Cenomanian (Bed 10) of Dunscombe. 



Section 4. — Quadrate. 

 Trigonia nodosa, Sowerhy, 1826. 



1822. Trigonia clavellata, G. Mantell (non Sotverby). Foss. S. Downs, p. 73. 

 1826. — NODOSA, J. de C. Sowerhy. Min. Conch., vol. vi, p. 7, pi. dvii, 



fig. 1. 

 ? 1840. — ciNCTA, L. Agassiz. Etudes crit. Moll. Foss. (Trigon.), p. 27, 



pi. vii, figs. 21, 23; pi. viii, figs. 2 — 4. 

 1844. — RUDis, A. d'Orbigny. Pal. Fran9. Terr. Cret., vol. iii, p. 137, 



pi. cclxxxix. 



