Remarks on the Trilohite. 33 



The anterior edge of the buckler of this species, as has been 

 often observed, is marked by a deep groove or furrow, produced 

 apparently by the junction of the upper and the under shell at 

 this place, and which at first sight looks like the mouth of the 

 animal ; indeed. Professor Brongniart calls the elevated ridges on 

 each side of this groove the lips. The mouth was, however, placed 

 no doubt much farther beneath. These lips^ perhaps, indicate the 

 separation of the shell, through which the trilohite crept out, and 

 left his cast-off covering in the same manner as recent crustace- 

 ans leave their exuvias. We know that the limulus polyphemus 

 creeps through a somewhat similar opening, made along the 

 whole anterior edge of his buckler.* In all our fragments, which 

 exhibit the under surface of the buckler, the lov/er lip is reflected 

 beneath, so as to form a kind of scroll or rolled edge, extending 

 from one side or angle of the head to the other. Beneath this, 

 and passing backwards towards the tail, the surface of the shell 

 is not flat and horizontal as in the isotelus and Umulus ; but it 

 swells up on each side, below the oculiferous prominences, into a 

 kind of oval pouch, diminishing in breadth as it recedes, and at 

 last terminates in a rounded point, below the second articulation 

 of the vertebral column. This is the position of the gullar pouch 

 or plate, when the animal assumes a creeping or swimming atti- 

 tude ; but when rolled up in the form of a ball, for the purpose 

 of defence, then the gullar plate being composed of a single 

 piece, and therefore not contractile, reached below the fourth ar- 

 ticulation of the back. Some of our specimens illustrate this 

 conformation in a very satisfactory manner. None of our frag- 

 ments exhibit fairly the small surface on each side of the gullar 

 plate, and the edge of the buckler beneath the eyes. This space 

 was probably slightly concave, and occupied with the mandibles 

 and their palpi, as in the genus serolis — the mouth being no 

 doubt placed near the rounded termination of the gullar pouch. 



Thus we have at last discovered nearly the whole inferior sur- 

 face of the buckler of the genus calymene, a portion which in- 

 cludes about one third of the animal. Not the slightest impres- 

 sion or other vestige of antennae can be perceived, and we may 

 therefore pretty confidently conclude, that this genus of trilobites 

 were destitute of those organs. Professor Demarest, in his his- 



* See Dr. Dekay. Annals of Natural History, vol. 1. 

 Vol. XXXVII, No. 1.— July, 1839, bis. 5 



