part 1] GAULT AND LOWER GREENSAND NEAR LEIGHTON. 77 



of the few confident identifications ' (Hawkins), appears to have been found 

 previously in England only in and just above the Upper Greensand ; and 

 Echinospatagtis aff. miircMsonianus (Mantell) (1 specimen) in the Upper 

 Greensand only. Both genera have many representatives in the Lower 

 Cretaceous, 



Cardiaster ? latissimus Agassiz (1 specimen) and C. cf . fossarius (Benett) 

 (2 specimens) are the largest urchins that have been found at Shenley, 

 measuring 1^ to 2 inches in diameter. Prof. Hawkins states that his 

 suggested identifications are ' given without any real confidence.' The first- 

 named species is a rarity in the Upper Greensand ; the second- named is one 

 of its commonest fossils ; but in North-Eastern France Holaster ( — Cardiaster) 

 latissimus is recorded by Jules Lambert as occurring occasionally in the 

 upper part of the Aptian (of Grandpre) and more generally in the Gault;^ and 

 in the South of France it is recognized by Kilian (op. cit. pp. 309, 362) as an 

 Aptian species. With respect to the Shenley forms, it is of importance to 

 note that an echinoid of similar type occurs in the undoubted Mammillatus- 

 beds at Grovebury. I collected there, from a gritty phosphatic nodule, an 

 imperfect cast (see p. 50), and another specimen of the same kind was 

 obtained by the Geological Survey ; Prof. Hawkins refers my specimen doubt- 

 fully to C. afP. latissimus Agassiz (op. cit. p. 57) and notes that the Survey 

 specimen, though not specifically determinable, agrees exactly with mine in 

 form and matrix (op. cit. p. 60). From the same nodules I obtained the casts 

 of Pseudodiadema comparable with one of the unidentifiable limestone fossils 

 (op. cit. p. 57). 



Pyrina cf. inflata d'Orbigny (1 specimen) ; P. cf. desmoulinsi d'Archiac 

 (2 specimens) ; P. aff. laevis Agassiz (3 specimens). These small urchins 

 may, according to Prof. Hawkins (antea, p. 48), be shape-variants of a 

 single species ; which presumably is the same as the P. desmoulinsi of some 

 of the Tourtias. The genus as at present defined is fully represented in the 

 Lower Cretaceous, so that its appearance under suitable conditions at the 

 base of the Gault is not anomalous. It may be noted that Pyrina cylindrica 

 A. de Grossouvre is recorded by C. Jacob (op. cit. p. 309) from the lowermost 

 beds of the Albian of Southern France. 



Cidaris hoiverbauM Forbes, is based, not on a test, but on three spines, and 

 the determination can hardly be reckoned conclusive. 



Conulopyrina anomala Hawkins, being a new genus and species (Geol. Mag. 

 1921, p. 420) has no present value for correlation. 



There is nothing among these echinoderms that seems to justify violent 

 stratigraphical methods of explanation. The collection being poor, negative 

 evidence has less weight here than in the case of the brachiopods ; but the 

 absence of most of the commoner Upper Greensand and Lower Chalk species 

 would be remarkable if the limestone were really newer than the Gault. 



The Crustacean Cyphonotus incertus Bell, mentioned by Dr. Kitchin 

 & Mr. Pringle, represents a comparatively rare type of fossil, respecting which 

 it must be unsafe to draw deductions from the scanty and imperfect material 

 at present available. 



In arguing for the Upper Greensand age of the glauconitic sand of Gar- 

 side's pit, the same writers mention Serpula antiquata J. de C. Sowerby as 

 ' a common fossil in the Pecten-asper zone of Wiltshire ' (K.P., p. 6), but do 

 not mention that it is also a fossil of the Lower Greensand and Red Chalk.^ 

 They also refer at some length to cirripede-remains from the same bed which 

 were submitted to Mr. T. H. Withers, who ' believes that the more advanced 



^ ' Eecherches sur les Echinides de I'Aptien de Grandpre ' Bull. Soc. Geo], 

 France, ser. 3, vol. xx (1892) p. 89. 



2 ' Geology of the Weald' Mem. Geol. Surv. 1875, p. 13 ; ' Gault & Upper 

 Greensand ' ibid. 1900, p. 476 ; and T. Wiltshire, ' The Eed Chalk of England ' 

 Geol. Assoc. 1859, p. 15 & fig. 



