NOTES ON THE CAMBRIDGE GREENSAND. 501 



however, reckon the number on the upper valve as 35 to 38, but 

 have not seen the lower valve. 



Pecten Dutemplei is said to have about 40 or 50 ribs on the upper 

 valve ; " and a small simple linear rib occurs between these ribs, 

 but not regularly." This arrangement is better shown in Pictet and 

 Roux's figure than in that of D'Orbigny ; and the number of ribs 

 given by the latter, viz. 70 to 80, is probably an exaggeration. 



Both P. aptiensis and P. Dutemplei have the same curious oblique 

 striation across the interspaces, and are in all other respects very 

 like one another, the chief difference mentioned by D'Orbigny being 

 the presence of the occasional intermediate simple rib on the latter 

 species. 



Now occasional simple ribs are also distinctly visible on some 

 specimens of P. Barretti, especially on that previously referred to 

 as having been mistaken for P. Espaillaci. P. Barretti, therefore, 

 would appear to be most nearly allied to the Grault form of the 

 species, viz. P. Dutemplei. 



Mr. Seeley finds some differences in the ornamentation of the ears ; 

 but his remarks regarding them (p. 119) are not very clear : neither 

 does the variation seem very important ; for the combination of 

 transverse and radiating lines is very frequent on the ears of allied 

 species, and sometimes one set of markings, sometimes the other, 

 stands out more prominently, according to growth and state of 

 preservation. 



All the differences above noted are merely slight variations from 

 the earlier type of P. aptiensis, under which head I think both 

 P. Dutemplei and P. Barretti should be ranged as varieties. The 

 latter has been found by Mr. H. G. Fordham in the Greensand at 

 Swanage. 



Pecten Rauliniantjs ? D'Orb. 



Pecten Raulinianus, D'Orb. Pal. Fr. iii. pi. ccccxxxiii. figs. 6-9. 



A specimen recently placed in the Woodwardian Museum is 

 about the same size as P. Barretti, but possesses very different 

 characters. No interstitial striations are visible ; the ribs are nume- 

 rous, and ornamented with closely set, narrow, lamellated imbrica- 

 tions. It appears to agree more closely with P. Raulinianus than 

 with any other known to me ; indeed, as far as can be seen, in 

 ornamentation it agrees exactly with that species. 



Pecten stjbactjtus, D'Orb. 



Pecten subacutus, D'Orb. Pal. Fr. p. 603, pi. 435. figs. 5-10. 



This species has about 25 simple ribs, ornamented with squamose 

 elevations set at short intervals ; the ribs are rounded on the upper 

 valve, but more angular and acute on the lower ; slight striations 

 run down each side of the ribs into the interspaces, which are 

 nearly as broad as the ribs. 



It is a very rare Pecten at Cambridge ; and most of those I have 

 seen were much worn, so that the ribs appeared quite plain ; but a 



