6 Prof. W. King ow Spirifer cuspidatus. 



of colour. Very few of them present a definite form, their outer 

 portion being generally irregular and lightest in colour, shading 

 off into the subtranslucency of the surrounding fibres*. It 

 is extremely rare to see the perforations pushing the fibres 

 aside ; the latter pursue their course, as it were, with very 

 seldom any appearance of being forced either to the right or 

 the left by the former. When the perforations are pale, it is 

 only by their being slightly less translucent than the fibres 

 that their presence can be with safety determined. Frequently 

 there are breaks in the lines of perforations ; and spaces, ap- 

 pearing to be imperforate, lie next to others undoubtedly per- 

 forated. In two of the sections no perforations are seen, 

 except perhaps what might be considered to be, in two or 

 three cases, the faintest traces of them. 



Whatever be the cause of the absence of the perforations in- 

 the preceding sections, the following additional points ought 

 not to be overlooked in considering this question : — (1) The 

 perforations often appear as if they stopped short of one of the 

 surfaces of the sections. (2) The sections often exhibit what 

 appear to be veiy minute perforations intermixed with the 

 ordinary-sized ones. (3) I have occasionally seen two fibres 

 appear as if crossing the transverse section of the perforations, 

 where the latter are faint. These points, and the indefinite out- 

 line of the perforations, the little or no deviation they produce 

 in the ordinary course of the fibres, also their "^«te7z?/ distribu- 

 tion " (in which the sections agree with those examined by 

 Meek and Carpenter), certainly do not ordinarily prevail 

 among perforated Palliobranchs, at least in recent species and 

 others, occurring in Tertiary and Secondary rocks, which have 

 undergone no metamorphism. 



It may noAV be mentioned that I ^' suspected " Spirifer cuspi- 

 datus to be perforated, from.^^ patches of faint, slightly raised, oval 

 impressions" being " present on the subsurface shell-layers " 

 of Mr. Birmingham's specimen — and that I expressed an opi- 

 nion of the ^' impressions " being each caused by the rising- 

 up of the fibres around a perforation, such as takes place in 

 Waldheimia australis and other recent species f- This rela- 

 tionship between the impressions and the perforations is proved 

 by the evidences illustrated in PI. II. Fig. 4 represents the 



* According to one of Mr. Meek's drawings, the perforations, as seen in 

 a variety, or an allied species {Sp. mbcu^pidatus), are distinctly defined — 

 so much so that Mr. Meek informs me that he has " in some instances had 

 under the microscope a single isolated fibre with half the diameter of a 

 perforation cut out on one side (shown in 1*1. III. fig. 3), as illustrated by 

 Carpenter in some of his publications." 



t Geological Magazine, June 1867. 



