504 Dr. A\'. B. Carpenter on tlie Structure of Brachiupud Shells 



I added, '' it is a matter of entire indifference whether Prof. King 

 does or does not admit the correctness of my observations ; but 

 I would submit, that the interests of science are not very hkely 

 to be promoted by this easy setting- aside of observations made 

 with every advantage of first-rate instruments and careful pre- 

 paration of specimens, in favour of glances with a hand-magnifier 

 at shells whose surfaces are peculiarly liable to present deceptive 

 appearances." 



As Prof. King made no reply to these observations at the 

 time they were published, I hoped that he acquiesced in their 

 justice, and that the question between us might be regarded 

 as settled. It now appears, however, that I was premature ; 

 since, after the lapse of two years. Prof. King returns to the 

 charge; not so much, however, to maintain his former asser- 

 tions, as to justify himself for having discredited mine. He 

 now admits the non-existence of perforations in Rh. psittacea, 

 and, by implication, in other Wiynclionellidce ; but he considers 

 the case of Rh. Geinitziana to be an unquestionable exception 

 to the universality of non-perforation in that genus, — both valves 

 of this species being " as distinctly and regularly perforated as 

 those of any Tej-ebratulidce.'^ By the kindness of Mr. Davidson, 

 I have had the opportunity of examining one of Prof. King^s 

 own specimens, as well as an authentic specimen of this species 

 which he has received from Baron von Schauroth ; and I am 

 bound to admit that both these specimens bear out Prof. King's 

 statement, so far as can be judged by external appearance. I 

 have not felt at liberty, however, to damage these specimens to 

 the extent necessary for determining the question whether the 

 superficial pittings extend through all the layers of the shell, 

 and are therefore the homologues of the perforations of I'ere- 

 bratulida. Supposing, however, this should prove to be the 

 case, it would still have to be determined whether, in spite of 

 its external characters, this species be a true Rhynchonella, or 

 whether it should be separated as a sub-type of that genus, 

 which, like Spirifer, may contain both perforated and non-per- 

 forated species, or whether, like String ocephalus, it should be 

 found to be more related in its internal structure, as well as in 

 the texture of its shell, to the Terebratulidce. 



The question of the accuracy of my ohservations on this point 

 is one quite distinct from that of the accuracy of my generaliza- 

 tions. I have given, in my Memoir, the evidence on which the 

 latter seemed to me to be at least provisionally established ; but 

 I myself remarked at its conclusion, on the necessity of a far 

 more extended examination of species than I had been myself 

 able to make, before these generalizations could be regarded as 

 established. I shall be, therefore, as ready as any one to with- 



