178 A. S. PACKARD, JR., ON THE 



Roemer " suggested the affinity of Eurypterus with Limulus ; pointing out, however, the 

 great difFerence in the feet, etc. 



In 1849, and again in 1854, McCoy united the Limulidse with the Eurypteridse in the 

 tribe Poecilopoda of the order Entomostraca. In 1856, Huxley compared Himantopte- 

 rus (Pterygotus) to the zoese of the Decapods, remarking that " The nearest approach to 

 Himantopterus which couhl be constructed out of the elements afforded by existing Crus- 

 tacea, would he produced by superinducing, upon the general form of a Cumoid Crustacean, 

 such a modification of the appendages as we find among the zoeaform Macruran larvee." In 

 1857, in his '' Lectures on Natural History," he remarks again : " I conceive, therefore, 

 that the Eurypterida must form a group by themselves, which are best understood by com- 

 bining together organic peculiarities, at present found only in the Copepoda, the Xipho- 

 sura, the DiastyUdce, and the larvoe of Podophthalmia." 



In 1859, Prof James Hall, in the " Palaeontology of New York, in," " containing," ac- 

 cording to Mr. Salter, "the fullest material for the illustration of this genus" (Eurypterus), 

 discussed more fully than any one else had done the close relation of Eurypterus to Limulus, 

 having shown satisfactorily the homologies of the " anomalous plates and processes ^ about 

 the position of which Prof Huxley and myself [Salter] were compelled to guess," i.e., that 

 they are homologous with the first pair of abdominal swimming respiratory feet of Limulus. 

 "All this was as satisfactorily made out by" a Russian naturalist, Nieszkowski [in the same 

 year]. "We [Salter] had also arrived at the same conclusion before Nieszkowski's admira- 

 ble paper had reached us." 



Professor Hall remarks that he is not prepared to agree with Huxley in the opinion that 

 this form and Pterygotus are related to Cuma and Mysis, and then says, "As my examina- 

 tions have progressed, and the parts now shown have gradually been brought out in their 

 true relations by the study of a large number of specimens, many structural analogies 

 with Limulus have been observed. At the same time, both in the form of the feet and in 

 the jointed body, the great dissimilarity with Limulus is apparent ; but I am not prepared 

 to maintain that these external differences are of ordinal importance." He then adds in a 

 foot note that Mr. Morris, in his " Catalogue of British Fossils," has arranged the Euryp- 

 teridse, including Eurypterus and Pterygotus, as a family following Limulidte, under the 

 same order. He then cites Professor Agassiz's opinion after an inspection of his speci- 

 mens, as follows : " This preeminent naturalist has given his opinion most unequivocally 

 that the Eurypteri are closely related to Limulus, belonging even to the same order. He 

 regards the antennal system as entirely absent. The organs of locomotion all belong to 

 the cephalic region ; and while externally they perform the functions of feet, they are at 

 their bases organs of manducation. The central organ, indicated as a locomotive append- 

 age, and attached to the lower side of the first segment. Professor Agassiz regards as 

 similar to the appendage attached to the membranaceous feet behind the swimming feet of 

 Limulus, and instead of being double, as anchylosed, as in young Limulus. Since my 

 comparisons, during investigations of these fossils, had been made almost entirely with 

 Limulus, I am prepared to appreciate these views of Professor Agassiz." 



1 Mr. Woodward, following Prof. Huxley, calls this the terus to Limulus, and decides, it seems to us, beyond any 



"thoracic plate, or operculum"; in reality it is the first pair reasonable doubt, that the two forms should be placed in 



of abdominal lamellate feet, and Hall's discovery is of the the same group, whether we call it suborder or order, 

 highest value in thus establishing the close affinity of Euryp- 



