130 PROC. COTTESWOLD CLUB vol. xiir. (2) 



only partiall}' surrounding the foramen ; beak area fairly 

 prominent ; hinge margin indenting the brachial valve. 

 Valves ornamented by a great number of fine rounded ribs 

 which extend from the beak to about two-thirds the length 

 of the shell, where they merge in from 8 to 10 prominent 

 angular ribs extending from about half-way along the 

 shell to the margin. Sinus and mesial fold well defined, 

 occupied by from two to four of the large ribs which are 

 usually somewhat unequal in magnitude. A large speci- 

 men measures in length 13 mm., in breadth 14 mm., and in 

 height 9 mm. 



Dr Davidson on p. 224 of the Supplement to his Mono- 

 graph of the Brit. Foss. Brach. states that Prof. Tate in 

 the Geological Magazine for Dec., 1869, quotes Rhym. 

 jurensis from the Zone of Am. opalinus, but does not 

 give the locahty. His (Prof. Tate's) authority appears to 

 be a record of Dr Lycett's in the Proceedings of this Club 

 (Vol. II., p. 142, i860), where it is stated to occur in the 

 Upper Zone of the Supra-Liassic Sands. Dr Davidson 

 goes on to say that he has seen the specimen referred to, 

 and has no hesitation in stating that it is referable to 

 R. rimosa of von Buch, and he gives a figure of it 

 (pi. xxvii., fig. 10). I agree with Dr Davidson that the 

 specimen figured is not R. jurensis, but I am unable to 

 agree with him that it is correctly called R. rimosa. I am 

 well acquainted with both R. rimosa and the shell figured 

 by Dr Davidson, and I am satisfied that they are not the 

 same. Moreover, R. rimosa has not certainly been found 

 in strata of later date than the Zone of Am. He^ileyi, 

 which is below the Marlstone of the Middle Lias, whilst 

 the form in question is confined to the Diimorticria and 

 Moorei horizons of the Cotteswold Cephalopod-bed, which 

 are very much later in date. 



