CARBONIFEROUS FOSSILS OF IRELAND. 



127 



DELTHYRIDiE. 



The Delt.hyrid(c or Spirifers (witli the exception of Ort/iix, not tlicn known) were originally formed into 

 the genus Spirifer by the late Mr. Sowcrby, who named them from the spiral appendages which he was the first 

 to figure and describe. This he did on the sujjposltion that they were " two spirally-rolled cones," and as such 

 he lias figured tliem, both in the Linnajan Transactions and Mineral Conchology, without, however. Indicating the 

 manner of their attachment to the shell, or their uses. The turns are so coated with little crystals of calcareous 

 spar in those figures, that they appear much thicker than they really are, and touching each other ; the conse- 

 (juence of which has been, that nearly all the continental geologists have described them as two hollow cones 

 floating free in the body of the animal. M. Deshayes considered them as the arms of the animal, and mistak- 

 ing the crystallization represented in Mr. Sowerby's figure for joints, he describes them as articulated (which 

 the arms of Brachiopods never are). Almost every author^ of the present day considers these appendages as the 

 arms of the animal. As I have been led to hold an entirely opposite view, it may be necessary to enter into some 

 details of the internal structure of the Spirifers, which I have arrived at by making a great number of sections 

 of the shells, and from the examination of several silicious casts, the calcareous matrix of which I succeeded In 



removing, by the action of dilute hydrocliloric acid, so as to display the parts with 

 great delicacy. 



In the dorsal, or large valve, we find two short, strong, cardinal, teeth (see fig. 14), 

 A A, one at each side of the base of the triangular foramen ; In order to give the 

 requisite strength to these teeth, we find them, in all the species, supported by two 

 thin, shelly plates, which extend from their bases to the beak of the shell, and rest 

 against the dorsal valve (b b). These I propose to call the dentdl lamellcB ; It Is 

 their bases which form the two diverging lines we so constantly find on grinding 

 down or polishing the beak of the large valve of the Spirifers (see fig. 14, lower 

 figure), they form the sides of the triangular foramen. In the centre and invariably 

 longer than these is a smaller septum (c). 

 In the ventral or smaller valve we find no septum, but the cardinal teeth, like those of the TerebratulcB, 

 are exceedingly complex, they arise one on each side the beak, by a broad, flattened base, from which they 



Fig. 15. 



Fig. 16. 



diverge as in the annexed cut (fig. 15) approximating again 

 at about the middle of the shell, where they give off a short, 

 blunt process, directed backwards ; they then diverge until 

 they reach the anterior margin of the shell, when they turn 

 backwards, and towards the beak forming a number of spiral 

 turns, diminishing in size towards the cardinal angles. These 

 are the bodies considered by most authors as the arm.? of the 

 uiiimal, but which I hope to be able to shew, are merely a 

 modification of that delicate, shelly support, which we find 

 in the true Terebratulce (see fig. 16), for the body of the ani- 

 mal. In the first place the arms of Brachiopods are analo- 

 gous to the foot of other bivalves, and therefore take their 

 origin from the body of the animal, not from the shell. I have 

 been able to demonstrate that the present organs arise from 

 the shell. In precisely the same position as the Internal sup- 

 port of the living Terebratulce. Mr. Sowerby describes the appendages of the Spiriferce, as " hollow, cartilagi- 

 nous tubes ;" In this It Is possible that he mistook the outer coating of minute crystals for the tube itself, and the 



* Tills was written nearly three years ago ; some of the views have been since adopted by others. 



