APPENDIX. 81 



On Tomocaeis Piercet, a eecent Isopod, dredged East of Cape Feio, by the late 

 Prof. L. Agassiz, offering affinities with the Teilobita. 



The following letter, from the late Prof. Agassiz to Prof. Pierce, of Harvard 

 College, 1 seems deserving of notice as recording the discovery of an abnormal 

 form of existing Isopod, having many points of affinity with the extinct Trilobita. 2 

 " In my first letter to you concerning deep-sea dredging, you may have 

 noticed the paragraph concerning Crustacea in which it is stated that among 

 these animals we may expect ' genera reminding us of some Amphipods and 

 Isopods aping still more closely the Trilobites than Serolis.' A specimen 

 answering fully to this statement has actually been dredged in forty-five fathoms, 

 about forty miles east of Cape Frio. It is a most curious animal. At first sight 

 it looks like an ordinary Isopod, with a broad, short, flat body. Tested by the 

 characters assigned to the leading groups of Crustacea, whether we follow Milne 

 Edwards' or Dana's classification, it can, however, be referred to no one of their 

 orders or families. As I have not the works of the authors before me, I shall 

 have to verify more carefully these statements hereafter ; but I believe I can trust 

 my first inspection. The general appearance of my new Crustacean is very like 

 that of Serolis, with this marked difference, however, that the thoracic rings are 

 much more numerous and the abdomen or pygidium is much smaller. It cannot 

 be referred to the Podophthalmians of Milne Edwards (which correspond to the 

 Decapods of Dana) because it has neither the structure of the mouth, nor the gills, 

 nor the legs, nor the pedunculated eyes of this highest type of the Crustacea, nor 

 can it be referred to the Tetradecopods of Dana (which embrace Milne Edwards' 

 Amphipods and Isopods), because it has more than seven pairs of thoracic limbs; 

 it cannot be referred to the Entomostraca, because the thoracic are all provided 

 with locomotive appendages of the same kind. But it has a very striking 

 resemblance to the Trilobites; it is, in fact, like the latter, one of those types 

 combining the characteristic structural features of other independent groups 

 which I have first distinguished under the name of synthetic types. Its 

 resemblance to the Trilobites is unmistakable, and very striking. In the first 

 place the head stands out distinct from the thoracic regions, as the buckler of 



1 ' Canadian Naturalist,' vol. vi, new series, 1872, p. 359. 



2 I am indebted to Mr. P. Beddard, Prosector of the Zoological Society of London, for calling my 

 attention to Tomocaris. Mr. Beddard informs me he has written to Cambridge, U.S., to inquire about 

 the specimen, but it has unfortunately been mislaid or lost, and no other has since been obtained. 



