214 Dr. W. B. Carpenter on Rhynchonella Geinitziana. 



XVIII. — On the Structure of the Shell of Rhynchonella Geinitzi- 

 ana. By William B. Carpenter, M.D., F.R.S. 



To the Editors of the Annals and Magazine of Natural History. 



Gentlemen, Feb. 17, 1857. 



I lose no time in communicating to you the result of an exami- 

 nation which I have this day been enabled to make, of the shell 

 of Rhynchonella Geinitziana, the existence of perforations in 

 which, " as distinct and regular as those of any Terebratulidae," 

 was positively affirmed by Prof. King, in your pages, about a 

 year ago (A. N. H. vol. xvii. p. 334). In my comments upon 

 Prof. King^s statements as to this and other points relating to 

 the shell-structure of Brachiopoda, I remarked (p. 504) that I 

 had seen enough to satisfy me that Prof. King had some grounds 

 for this assertion, but not enough to satisfy me that the perfora- 

 tions extend through the entire thickness of the shell, and are 

 therefore the equivalents of those of Terebratulidse. In order to 

 determine this question, specimens are required in which the 

 shell has neither been reduced by abrasion on its external sur- 

 face, nor has had its original texture obscured by metamorphic 

 action. I had strong reason to believe that in one or both of 

 these particulars the specimens at my command were faulty, and I 

 therefore abstained from committingmyself to apositiveconclusion. 



The sequel has proved the justice of my caution. Mr. David- 

 son has taken the trouble to send all the way to Russia for the 

 specimens of this rare shell contained in the collection of the 

 Corps des Mines of St. Petersburg ; and these have been kindly 

 forwarded by General Von Helmersen, the head of that establish- 

 ment, for the express purpose of being examined by me. 



From among the four specimens thus placed before me (which 

 are guaranteed by Mr. Davidson to be specifically identical with 

 the German specimens examined by Prof. King), I selected the 

 one which presented on its exterior the least indication of abra- 

 sion or metamorphic action ; from this I carefully removed some 

 shreds large enough for microscopic determination ; and I am 

 now in a condition to assert positively, that portions of the ex- 

 ternal laminse of Rhynchonella Geinitziana, in which the peculiar 

 texture of the shell is perfectly preserved, do not shotv the least 

 evidence of perforations, — the so-called perforations of Prof. King 

 being therefore only pits upon the internal surface of the shell, 

 analogous to those which present themselves upon the external 

 surface of Porambonites and Trematis. 



T shall be happy to submit this preparation to the inspection 

 of any one who may feel an interest in the question, and remain. 

 Gentlemen, your obedient Servant, 



William B. Carpenter. 



