﻿Vol. 6 1.] 



PHOSPHATIC CHALK OF TAPLOW. 



473 



staining at their edges. Where more exposed, the rock rapidly 

 exfoliates, and the fossils are much less apparent on the convex 

 faces of the blocks. 



These beds have yielded : — 



Pisces, (v. c.) 



Corax falcatus, Ag. (c.) 



Corax pristodontus (?) Ag. 



Lcmna appendiciUata, Ag. (e.) 



Oxyrhina sp. 



Actinocamax granulatus (Blainv.) (v.c.) 



Inoceramus Cuvieri, Sow. (c.) 



Osfrea hippopodium , Nilss. (c.) 



Os/rea vesicidaris, Lam. (v. c.) 



Ostrea Wegmanniana, d'Orb. (v. c.) 



Ostrea spp. 



Pecten Nilssoni, Goldf. 



Plicaiula sigittina, S. P. Woodw. (c.) 



Spondylus lotus, Sow. 



Entalophora Pergensi, Greg. 

 Scalpellum fossula, Darw. 

 Serpula plana, S. P. Woodw. 

 Echinocorys scutatus, Leske. 

 Echinocorys scutatus, var. (cf.) pyrami- 

 ded tus, Portl. (c.) 

 Cidaris sceptrifera, Mant. (r. c.) 

 Galerites (?) . 



Micraster cor-anguimtm, Klein, (c.) 

 Marsupites testudinarius, Schloth. (v.c.) 

 Asteroidea. 



Porosphcera globular is, Phil. 

 Plants (?). 



The plates of Marsupites (nearly all incomplete) are of the patterns 

 usually found in the midst of the Ma rsiqntes-'B and \: the bulk of 

 them exhibit a well-marked divergent ridging, and the remainder 

 a faint tuberculation, or blnnt radial plication. A plate of the last- 

 named type was found about 1 foot below the top of the Brown 

 Chalk, and the others within a distance of 2 feet above the bottom. 

 The distribution of Marsupites in the Upper Brown Chalk, therefore, 

 much resembles that of Uintacrinus in the Lower. 



The abundance of guards of Actinocamax granulatus at all levels 

 is most remarkable, and, we believe, quite unexampled in the Chalk 

 of this country. One of us has observed as many as seven, in a 

 space estimated afc rather less than 60 cubic inches. The majority 

 are distinctly granulated, the stouter forms often very markedly so, 

 and their size is, on the whole, rather below the average of the 

 examples found in the Micraster cor-anguinum and Marsupites- 

 Zones of other English sections. 



Owing to differential movements within the beds (which have 

 frequently fractured and ' faulted ' the guards, and crushed their 

 weaker proximal ends) and to the difficulty of extraction from 

 a rock which is at once tough and brittle, not more than 10 per 

 cent, of our examples are whole. In these, the depth of the alveolar 

 cavity ranges from a ninth to a fifth of the length of the guard, the 

 average ratio being about 1 : 7. 2 



Taking into consideration all those examples, complete or other- 

 wise, in which the anterior end is well preserved, the alveoli have, 

 generally, a more markedly-quadrate section, and a greater depth, 

 than those of the guards of Actinocamax granulatus from the 



1 For a definition of this term, see A. W. Eowe, ' Zones of the White Chalk, 

 &c. Pt. I ' Proa Geol. Assoc, vol. xvi (1900) p. 296. 



2 The importance of stating such measurements, in all cases where the species 

 is doubtful, will be gathered from a perusal of M. A. de Grossouvre's ' Obser- 

 vations sur les Belemnitelles, &c. ' Bull. Soc. Geol. Prance, ser. 3, vol. xxvii 

 (1899) p. 129. 



