INTIMATE STRUCTURE OF THE SHELLS OF BRACHIOPODA. 31 



is of typical value as affording an absolute distinction between certain families, possesses a 

 greatly inferior value as regards others; thus we shall find that both Spiriferida 

 and Strophomenida contain perforated and non -perforated shells ; and it will be for further 

 investigation to determine, whether the character has here a generic value (serving, for 

 example, to distinguish Spiriferina from Spirifer, Orthesina from Orthis), or whether it must 

 here rank as a mere specific difference. The details which I shall presently furnish, may 

 help towards the determination of this point ; but it will require a far more complete and 

 extended investigation than I have had either time or opportunity for making, to determine 

 the real import of this character in every group in which it seems to be otherwise than 

 constant. 



Such an investigation, however, to be of any value, must be made with great care ; 

 superficial observations being here worse than useless, because they are hable to give the 

 most erroneous results. The perforations in the shells of fossil Brachiopoda are very 

 liable to be filled-up by the matrix ; and such a smoothness and apparent continuity may 

 thus be given to their surfaces, that no '' punctuations " may be perceptible by the 

 microscopist, still less by the observer who is armed only with a hand-magnifier. On the 

 other hand, the surface of some shells is marked in such a manner, as to indicate the 

 presence of the perforations with almost absolute certainty to any one who has not 

 learned caution from previous experience ; yet the infallible test of a transparent section, 

 examined under a sufficient magnifying power, makes it evident that there is not the 

 shghtest vestige of real perforations, and that the supposed " punctuations" are nothing 

 else than surface-markings, analogous to the " sculpture '' of other shells. Of the im- 

 portance of such precautions, a very remarkable example is afforded by the existence of 

 perforations in Striffocephalus, which has been uniformly regarded as a non-punctuated 

 shell, and placed among the Rhynconellidse, whilst its real position (as the presence of 

 perforations would indicate) has been found by Mr, Davidson to be among the Terebratulidae. 

 Conversely, the perforations are really wanting in Poramhonites reticulata, notwithstanding 

 that there is a most decided and regular " pitting " of the surface of the shell, extremely 

 resembling the large punctuations of some of the Terebratulidae and Spiriferidse ; the 

 place assigned to this genus on other characters being among the Rhynconelhdse, the 

 existence of perforations in its shell would have been anomalous.^ 



1 I lay the more stress on the importance of this method of examination, because an attempt has 

 been made by Professor King (Monograph of the Permian Fossils of England) to put aside my former 

 observations, made with adequate microscopic power upon transparent sections of the shells, as altogether 

 valueless, on the strength of an examination of their surfaces with a Stanhope-lens. "Dr. Carpenter," 

 he says (p. 110, note), "places Hypothyrises (RhynconellBe) in his non-perforated division of the 

 Brachiopods ; but punctures, although mucli more minute than those in the Terebratulidae, occur in every 

 species that has passed under ray notice. Punctures also occur in Productidce and Spiriferidce ; in short, 

 7 doubt their absence in any Brachiopod whatever'^ — Now I have Professor King's own authority for 

 stating, that he has relied entirely on superficial observations made with a hand-magnifier, than which, as I 

 have shown above, nothing can be more fallacious ; and further, that he has never himself examined the 



