﻿300 f DR. STANLEY SMITH ON AVLINA BOTIFOBMIS, [vol. lxxii, 



2. Sarcinula tiibeeosa : Specimen 212 ; found in Derbyshire, 

 and presented by W. Hopkins. (PI. XXIII, figs. 4 & 5.) 



The holotype is a silicified specimen, 'perforated by several large 

 drusy cavities. The coral structures' are nevertheless well pre- 

 served, and the interstices are but incompletely filled with 

 mineral deposit. The distal surface, which is in a fair state of 

 preservation, displays in a somewhat exaggerated form a mam- 

 millate development. The thecae are slightly larger than usually 

 observed, and the columella is not very prominently shown in 

 the transverse section (PI. XXIII, fig. 5). The number of 

 septa present is smaller than is generally the case, being only 

 about 30 : otherwise the characters of this form are in agreement 

 with those of O. phillipsi. 



Its one pronounced and distinguishing feature — the mammilli- 

 form calices — may be found associated in a single corallum with 

 calices of the iypes illustrated as typical of O. phillipsi. It 

 seems therefore inadvisable to regard the form, sirnply because 

 of its external characters, as a separate and distinct species. 



McCoy illustrated (from a fragment of the type) what he con- 

 ceived to be the internal characters of the species (' British Palaeo- 

 zoic Fossils ' pi. iii b, fig. 8 a), but he omitted the columella, 

 and showed the tabulae as concave — an idea probably due to the 

 tangential nature of the sections, which missed the former, and 

 incompletely displayed the character of the latter. 



ORIONASTRiEA PLACENTA (McCoy). 



1849. Sarcinula placenta F. McCoy, Ann. & Mag. Nat. Hist. ser. 2, vol. iii, 

 p. 124. 



1851. Sarcinula placenta F. McCoy, 'British Palaeozoic Fossils' p. 110 & 

 pi. iii B, tigs. 9, 9 a, 9 b. 



See also synonymy and notes on O. phillipsi. 



O. placenta differs from O. phillipsi solely in the absence of a 

 columella, and consequently in the form of the tabulae, which, 

 deprived of their axial support, are concave instead of being 

 conical. The major and the minor septa are almost equal in 

 length, the former advancing very little farther beyond the theca 

 than do the latter. 



O. placenta bears the same relationship to O. phillipsi as the 

 non - columellate forms of Lithostrotion (Diphyphyllum and 

 Stylastrcea) 1 do to the columellate forms. 



At certain horizons (for example, at the base of the Great 

 Limestone around Chollerford, South Northumberland) ' Diplxy- 

 phyllum' 1 not infrequently occurs to the exclusion of Lithostrotion 

 locally. It is conceivable that similarly O. placenta may subse- 

 quently be found, to the exclusion of O. phillipsi, at some particular 

 place or level. 



1 See W. Lonsdale, in E. I. Murchison's ' Geology of Russia, &c.' vol. i 

 (1845) pp. 619 & 624 : Diphyphyllum refers to the fasciculate, and Stylastrsea 

 to the massive, variety. 



