230 FAMILY GLOBIGERINIDA. 



uncertainty,* I have thought it just to Prof. Williamson, who has accurately described and 

 figured (ex, p. 46, figs. 80 — 89) the recent form that best elucidates the structure of these 

 fossils, to adopt the generic name Patellina which he has conferred upon this. I shall first 

 give an account of the recent type F. corrugata, partly based on Prof. Williamson's obser- 

 vations, and partly on my own examination of more developed specimens obtained by Messrs. 

 Parker and Rupert Jones from the coast of Australia ; and shall then describe the fossil types 

 on the basis of Mr. Carter's observations and my own. 



404. Patellina corrugata : External Churacivrs and Iiitenial Slnicture. — This very 

 beautiful but very minute shell has the form of a depressed cone, resembling that of a Patdia, 

 its diameter being twice or three times its height ; the apex of the cone is occupied by the 

 primordial segment; and its regularly chambered structure forms only a thin shelly wall, the 

 interior of the cone being more or less completely filled up by an irregular growth of secondary 

 chambers. In the British form of this type, the primordial segment is surrounded by two or 

 more turns of an irregular spiral (ex, fig. 90 a,) reminding us of the outspread spiral of Pul- 

 vinidina vvrmlcuhita (^ 3G6) ; and the subsequent growth of the cone is effected by the 

 addition of semi-annuli which interdigitate with one another (ex, figs. 87, 88), so as to present 

 a certain resemblance to Textidaria in plan of increase. Each annulus or semi-annulus 

 is described by Pi'of. Williamson as being divided into chamberlets by transverse secondary 

 septa, which spring from the external margin and pass towards the internal, but which do not 

 quite reach it ; so that all the chamberlets thus formed communicate with each other by a 

 continuous passage left along the internal side of the chamber (ex, Fig. 90). This partial 

 subdivision is marked externally by a crenulation of the surface. The secondary septa in the 

 British specimens are very commonly wanting, or are merely rudimentary, in the early 

 vermiculate spiral portion of the cone. Prof. Williamson expresses himself as unable to 

 determine in what mode the principal semi-annular chambers communicate with each other. 

 The diameter of his specimens of this organism does not exceed I -80th of an inch. — In the more 

 highly developed Australian forms of this type, on the other hand, which sometimes attain a 

 diameter of nearly l-25th of an inch, the growth is cyclical from its commencement; the 

 primordial segment being encircled by a circumambient segment, as in OrbUolites (^ 157)^ 

 which is often itself partially subdivided, and from which a complete annulus of segments is 

 givenoff (Plate Xlll, tig. 16) ; and I tind no trace of any subsequent division into semi-annuli, 

 resembling that described by Prof. Williamson. Moreover, 1 tind that the partitions between 

 the chamberlets are complete, not merely extending to the margin of the preceding annulus, 



* D'Orbigny's definition of CycluUna (Lxxrii, p. 139) is so nearly applicable to OrbitoUtes, that 

 Mr. Carter was formerly (xix) misled into characterising as a Cyclolina what I have shown to be a mere 

 variety of OriJio/i/es, and was further misled into characterising the white limestone in which this occurs 

 as Cretaceous instead of Eocene ; so that, as he has truly remarked (xxui a), "It would have been 

 better if M. D'Orbigny had never written anytliing about Cyclolina, than just enough to mislead." 

 There is, in fact, nothing either in his figures or descriptions of this fossil that enables us to identify 

 it with any certainty; its geological position being the chief point which differentiates it from OrbitoUtes, 

 and which renders it probable that it is to be associated with those subconical Orbitolince which seem 

 properly to belong to the genus Patctlina. 



