254 King — On Perforated Spiriferidce. 



represented are to be accepted as positive evidences of a perforated 

 structure; but they bear so strong a resemblance to ratber ill-defined 

 markings, undoubtedly arising from perforations, often seen on meta- 

 morphosed specimens of Dielasma hastata, and other allied carbon- 

 iferous species, in their form and arrangement, as to render the 

 existence of such a structure extremely probable. 



To show the resemblance between the impressions in Spirifer 

 cuspidatus, and those due to the canal-system in Dielasma hastata, I 

 have given a representation of the latter (See Woodcut, Fig. 2). 

 They consist, in both cases, of ovals slightly in relief, and separated 

 from one another by narrow depressed interspaces ; without, however, 

 any traces of perforations : they are present on different sub-surface 

 shell-layers. 



In palliobranchiate shells, as they usually occur, the outer-surface 

 of the valves often exhibits the opposite^ condition, being marked 

 with excavated ovals, each of which shows a perforation in the middle : 



o * y 

 o 



Tig. 1. Kg. 2. Pig. 3. 



the internal layers, however, present precisely the same general ap- 

 pearances observed in the above-named fossils, with the exception of 

 being perforated. The condition alluded to is clearly caused by the 

 fibres or prisms, which compose the shell-substance of the valves, 

 rising up around the walls of the perforations, as may be readily seen 

 in sections, both horizontal and perjDendicular, of Waldheimia Aus- 

 tralis, and other recent species. Suppose the perforations and 

 fibres of the latter to be obliterated by metamorphic action, or 

 mineralization, there would then be presented simply the raised 

 impressions similar to those occurring in the fossil species. 



Sufficient evidence has now been adduced to show my suspicion 

 to be well grounded; also, that Mr. Meek's opinion is so far 

 strongly supported. 



Like Mr. Davidson, I am not disposed to place Spirifer cuspidatus 

 in the genus Cyrtina ; but if it be really perforated, and there be any 

 physiological value in the perforations, genus-makers will find in this 

 species another of the many puzzles that beset their labours. Perhaps, 

 after all, it may be an aberrant species of Cyrtina, the median or 

 arch-supporting plate having been arrested in its growth through 

 atrophy, as appears to have been sometimes the case with the dental 

 plates in the genus Spirifer. 



No doubt Dr. Carpenter had some grounds for introducing my 

 name into his letter which has lately appeared in vindication of his 

 " original determination," on account of the mistake I made in 

 asserting that certain imperforate palliobranchs are perforated, — 

 a mistake which was duly acknowledged in one of my papers pub- 



