18 CRETACEOUS LAMELLIBRANCHIA. 



author are apparently all casts, so that an exact comparison cannot be made. 

 Geinitz considers that specimens which he obtained from the Planerkalk of 

 Strehlen and Weinbohla, and from the Planermergel of Walkmiihle near Pirna, 

 belong to N. pectinata ; but they appear to differ from the English specimens in 

 that the posterior part of the shell is rounded and relatively longer. 



The variations seen in different examples of this species are chiefly in the 

 proportions of length and breadth, and in the form of the curve of the ventral 

 margin, the latter giving to the shell a triangular or a rhomboidal outline. 



N. striatula, Romer, 1 N. truncata, Nilsson, 2 and N. Blochmanni, Geinitz, 3 have 

 been regarded by Geinitz and Reuss as identical with N. pectinata, Sowerby. 



Types. — The types, now in the British Museum, are labelled " Sussex." The 

 specimens figured by Man tell (except fig. 5) and those figured by Gardner are 

 likewise preserved in the British Museum. 



Distribution. — Through all the zones of the Gault at Folkestone ; Gault of 

 Burham, Aylesford, Black Ven, Devizes, Campton (East Bedfordshire), Ely and 

 Haddenham (Cambs.) ; Marls with Bel. minimus at Speeton ; Upper Greensand 

 of Warminster (cast only seen). 



Nttcula pectinata, Sowerby, var. cret2E, Gardner, 1884. Plate III, figs. 14 a, b, 15. 



1884. Nucula pectinata, var. cretj;, J. S. Gardner. Quart. Journ. Geol. Soc, 



vol. xl, p. 132. 



Remarks. — This form appears to differ from N. pectinata, Sowerby, only in 

 being proportionately shorter. The surface of the shell, in the two specimens 

 which I have seen, is somewhat abraded, but I do not think that the ornamentation 

 differs from that of N. pectinata. 



Without more examples I am unable to say whether this form is really distinct 

 from N. pectinata. 

 Measurements : 



Length 15 mm. 



Height 12 „ 



Thickness 9 „ 



Types. — In the Museum of Practical Geology (Nos. 6449, 6450). 

 Distribution. — Blackdown Greensand. 4 



1 'Die Verstein. der norddeutsch. Kreidegeb.' (1841), p. 68, pi. viii, fig. 2G (the type comes 

 from the Planerkalk of Strehlen). 



2 'Petrif. Suecana* (1827), p. 16, pi. v, fig. 6. 



3 ' Char, der Scliicht. u. Petref. d. sacba. Kreidegeb.,' pt. ii (1840), p. 50, pi. x, fig. 8. 



4 Erroneously stated by Gardner to come from the Ore;/ Chalk of Devon. 



