Refnarks on the Trilohile. 35 



or under surface of the buckler. By this peculiar mechanism, 



whenever the animal rolled itself into a ball, to give protection 



to the soft parts of the abdomen, the protuberance under the 

 shield would be introduced into the cavity below the tail, and 

 thus retain the whole shell in a fixed position. In this position 

 with the tail closed upon the buckler, the calymene is often 

 found. 



Professor Wahlenberg considers those trilobites only as perfect 

 animals, which are found rolled, the others being merely exuded 

 or cast-off shells, and in such alone, he remarks, can we expect 

 to discover the organization of the inferior surface. Most of the 

 fragments from Berkley Springs, which have occasioned my pre- 

 sent remarks, are found rolled up or partially coiled animals. All 

 trilobites have not, however, this power ; indeed, it seems to be 

 principally confined to those only whose extremities are rounded 

 and nearly equal in size. The rolled position would aflbrd to the 

 paradoxides and to many of the asaphs, but Uttle security against 

 the attacks of their enemies, and we rarely if ever find them in 



this attitude. 



Wahlenb 



though illustrated by the specimens now under consideration^ we 

 think of far too general a nature. 



The deep cavity beneath the tail in the fragments which we 



as tar as 



ninth articulation of the back ; in other words, a portion of it lies 

 beneath the three last abdominal divisions. It will be recollected 

 that the gullar pouch reaches below the fourth articulation of the 

 back, and that tlie whole number of divisions in the vertebral 

 column in the genus calymene, is twelve ; we have therefore 

 discovered in these fragments almost the whole of the inferior 

 surface, except the portion which lies below the five articulations 

 of the back commencing with the fifth from the buckler or shield ; 

 what we shall offer in regard to this portion of the animal must 

 be merely hypothetical, or founded on certain analogies of struc- 

 ture which probably existed between living crustaceous animals 

 and the fossil remains of such as inhabited the most anci^it seas. 

 Some of our fragments, we think, exhibit a transverse section 

 of our trilobite, showing the position and figure of the abdominal 

 cavity which once contained a portion of the viscera of the ani- 

 mal. One of the sections is through and parallel with the sixth 

 articulation of the back : by this means we have discovered that 



