Vol. 52.] A DELIMITATION OF THE CENOMANIAN. 153 



Calypso of d'Orbigny, described in his < Prodrome/ vol. ii. p. 167, as 

 very near ( 4 voisiae ') to L. Hoperi, but with more numerous punctated 

 grooves, and occurring in the Cenomanian of Rouen. 



Corbis rotundata, d'Orb., ■ Pal. Fr. Terr. Cret.' vol. iii. p. 113, 

 pi. 280. 



This is another shell, occurring in the Devon zone of Ammonites 

 Mantelli, which the acquisition of French specimens has enabled us 

 to identify. We should mention, however, that Mr. Meyer has 

 specimens which he had previously determined to be C. rotundata. 

 It is common in the sandy fades of the Cenomanien at Yimoutiers, 

 Gace, and Mortagne, though the shell so often remains in the matrix 

 that it is difficult to obtain more than casts of it ; the same is the 

 case in Devon, but a comparison of the casts leaves no doubt as to 

 the identification. 



Arca ligeriensis, d'Orb., 'Pal. Fr. Terr. Cret.' vol. iii. p. 227, pi. 317. 



This is another common shell in the French Cenomanian which 

 had been detected in the Devon beds by Mr. Meyer. Having 

 obtained several casts of it from Yimoutiers and elsewhere, we are 

 also able to state that it is common in the hard rocky basement-bed 

 of the Lower Chalk at Chard (commonly called l Chloritic Marl '). 



Trigonia affinis, Sow. 



This species was at first regarded by Lycett as only a variety of 

 Tr. excentrica, Park, (see ' Brit. Foss. Trigoniae,' Pal. Soc. Monogr. 

 p. 94), but in his Addenda (p. 187) he separates it again, and points 

 out the characters by which it is distinguished. The only specimens 

 which he refers to this species are one said to have come from 

 Blackdown, now in the Jermyn Street Museum, one from Ualdon 

 (Mr. Yicary), and one in Mr. Meyer's collection, from near Axmouth, 

 which Mr. Meyer informs me came from his Bed 12, the upper part 

 of our zone of Ammonites Mantelli. It is therefore a rare shell. 



Trigonia d tjnscombensis, Lycett, ' Brit. Foss. Trig.' Pal. Soc. Monogr. 

 p. 188, pi. xl. figs. 5, 6. 



This species was entered in Mr. Meyer's list of 1874 as ' sp. 

 allied to Tr. sinuata, Park.,' and was described as a new species by 

 Lycett in 1877. Mr. Meyer informs us that it occurs throughout 

 the zone of Ammonites Mantelli, in his Beds 10, 11, and 12, at 

 Dunscombe, Branscombe, WhiteclifT, and Pinhay. 



It is allied to Tr. affinis and Tr. excentrica, but though he dis- 

 tinguishes it from these, Lycett does not attempt to disentangle the 

 foreign synonyms, neither does he record Tr. dunscombensis from any 

 other localities. Under Tr. excentrica he gives the Tr. sinuata, Park., 

 in d'Orbigny as a synonym, and notes that d'Orbigny records this 

 Tr. sinuata from the lower beds of his Terrain Turonien (i. e. Ceno- 

 manien) at Le Mans, St. Calais, and Condrecieux in the Sarthe. 

 "We have not been able to obtain specimens of this Tr. sinuata, but 



