PECTEN. 217 



widely separated — in /'. quinquecostatus these ridges are continued from the ribs 

 across the grooves without change. See also /'. striato-costatus (below). 



Remarks. — The figure of Pecten sexcostatus given by Woodward is not suffi- 

 ciently good for exact determination, but specimens which have been obtained 

 from the same locality as the type leave no doubt as to the identity of /'. sexcos- 

 tatus with Janira Dutemplei, D'Orbigny. 



The examples from the Lower Chalk are regarded by Peron as specifically 

 inseparable from those found in the Upper Chalk, and with this view I agree, but 

 since some slight differences are generally noticeable, I think it maybe well to look 

 on the examples from the Lower and Upper Chalk respectively as two forms or 

 varieties of the same species, which may be referred to as Form a and Form (3. A 

 careful comparison of good series of specimens can scarcely leave any doubt on the 

 mind as to the later forms having descended directly from the earlier. The 

 examples found in the Gault probably also belong to Form a ; they have, however, 

 usually been referred to P. (Neil/tea) quinquecostatus. 



The strength of the main ribs and the convexity of the right valve vary 

 considerably in different specimens. There are also variations in the number of 

 intermediate ribs, in their relative sizes, and in the depth of the incisions of the 

 margin between the main ribs. In some examples from East Harnham the main 

 ribs are unusually strong. In some of the larger specimens from Norwich the 

 number of ribs near the margin of the valve is greater than usual owing to the 

 introduction of small ribs in the grooves. 



Types. — Woodward's type appears to have been lost. D'Orbigny's type of 

 Janira Dutemplei came from the Senonian of Chavot (Marne). 



Distribution. — Form a. — Chalk Marl of Dover, Folkestone, and Ventnor. 

 Totternhoe Stone of Burwell. H. subr/lobosus zone of Cherry Hinton. 



Form j3. — A. quadratus zone of East Harnham (Salisbury) and Winchester. 

 B. mucronata zone of Ballard Head (Dorset), Clarendon (Salisbury), and Norwich. 

 Upper Chalk (? zone) of Brighton. Recorded by Howe from the M. cortestu- 

 dinarium and M. cor-anguinum zones of Thanet. 



Pecten (Neitiiea) striatocostatus, Goldfuss, 1 18:3:3. Plate XLI, figs. 9, 10. 



A portion of a right valve and a nearly perfect left valve, which were found by 



1 'Petref. Germ.,' vol. ii (1833), p. 55, pi. xciii, figs. 2 c, d, e (not 2 a, h,/. g) ; Favre, ' Moll. Foss. 

 Craie do Leniberg' (1869), p. 156, \A. xiii. figs. 12, 13 ; Holzapfel, ' Moll. Aa.lwu. Kreide ' ( 1889), p. 239, 

 pi. xxvi, %. 19; Vogol,'Holl;indiseli. Kroido' ( 1S!I5), p. 2<l; Mill lor, 'M-llusk. Untorson. v. Braunschweig 

 u. Ilsede' (1898), p. 37 ; Bavn, 'Mollusk. i Danmarks Kridfcaflej.' ( 1902), p. 95, pi. ii, figs. 8, 9 ; Wolle- 

 mann, 'Fauna der Liineburg. Kreide' (1902), p. <;:;. 



