182 BRITISH FOSSIL CRUSTACEA. 



organs, want the appendages to the sixth abdominal somite, and present on some parts 

 of the body a remotely similar sculpture. In this order, however, we find but a small 

 labruin — a rudimentary metastoma — a very differently constructed body, and a large 

 number of appendages, both thoracic and abdominal, characters which effectually pre- 

 clude the association of the extinct Crustacea under discussion with this type." He 

 adds in a note : " If the abdominal somites of the Carboniferous Bellinurus, &c, were 

 really free, they would present a certain approximation to the Pterygoti. Indeed, the 

 evidence that these Carboniferous Crustacea were true Pcecilopoda is, to my mind, any- 

 thing but conclusive " (op. cit., p. 34). 



One serious difficulty in homologising the structures of Limulus and Pterygotus, 

 which no doubt weighed strongly with Messrs. Huxley and Salter against the classifica- 

 tion proposed by McCoy, arose from their having erroneously placed the large bilaterally 

 symmetrical plate (which we now know to be the thoracic plate or operculum) on the 

 front ventral surface of the head-shield, and named it " the conjoined metastoma and 

 labrum." 1 This mistake was, however, pointed out and corrected later on in the same 

 year (1859) by Professor James Hall, of Albany, U.S. (in his ' Palaeontology of the State 

 of New York '), 2 whose researches into the structure and affinities of Eurypterus, Pte- 

 rygotus, and Limulus, have led him to the conclusion that a close relationship exists 

 between them, and in this opinion he is supported by Professor Agassiz, 3 who believes 

 them to belong even to the same order. " He regards the antennal system as entirely 

 absent. The organs of locomotion belong to the cephalic region ; and while externally 

 they perform the functions of feet, they are, at the base, organs of manducation. The 

 central organ indicated as a locomotive appendage 4 (by Hall), Professor Agassiz regards 

 as similar to the appendage attached to the membranaceous feet, behind the swimming 

 feet of Limulus, and instead of being double is anchylosed as in young Limulus" 



Three years later I devoted much time to the examination of these forms, and with- 

 out being aware of the already published views of Professors Hall and Agassiz, I arrived 

 independently at the same conclusions with them. Fortunately, however, just as I was 

 about to publish them in 1863, 5 I became aware of Professor Hall's observations, and 

 was delighted to discover, that, if not the first to interpret the structure and affinities of 

 these interesting forms, I had at least excellent confirmation as to the correctness of my 

 views. 



In the same year (1863) Mr. W. Hellier Baily, F.G.S., Acting Palaeontologist to the 

 Geological Survey of Ireland, published his " Remarks on some Coal-measure Crustacea 



1 See Mr. Salter's restoration of Pterygotus anglicus, made in 18.59 for Murclrison's ' Si] una,' and 

 reproduced in Part I, p. 27, of this Monograph. 



2 Hall, ' Natural Hist, of New York : Paleontology ' (1859), vol. iii, p. 393. 



3 Op. cit., p. 394. 



4 The median appendage of the thoracic plate or operculum. 



5 See article " On the ' Seraphim ' {Pterygotus anglicus) and its Allies," by H. Woodward, in 

 ' Intellectual Observer,' 18G3, vol. iv, p. 229 (with a plate and a series of woodcuts). 



