224 BRITISH FOSSIL CRUSTACEA. 



cannot at present be established, and perhaps may always remain doubtful. It is also 

 impossible at present to say anything definite concerning the relationship between them 

 and the Arachnida. Therefore all we can do is to combine these three families under a 

 common name, for which I would propose Hackel's expression ' Gigantostraca,' and to 

 place them in the system beside the Crustacea." 



To conclude, then : 



According to Dr. Packard there is a Nauplius-stage passed by Limulus in the egg. 

 (He, however, does not seem quite to understand what is meant by a Naupliform larva.) 

 He admits that it is not like the " Nauplius " of Apus or of Branchipus, but is to be 

 compared rather to that of the Trilobites, a knowledge of which we do not possess. 



If Limulus is brought nearer to Trilobita through the discovery of the specimens of 

 Asaphus by the late Mr. E. Billings, F.G.S. (figured in ' Quart. Journ. Geol. Soc.,' 1870, 

 vol. xxvi, p. 479, pis. xxxi and xxxii), we have failed to understand its nature. The 

 specimen is believed to possess eight pairs of five-jointed walking-feet attached to the 

 movable thoracic segments of the body, not a series of mouth-feet (gnathopodites), as in 

 Limulus, but rather like the thoracic legs in the Isopoda. 



That which really does bring the Trilobites near to Limulus is the series of embryonal 

 •changes passed through by the latter in the egg, which resemble the young of the former, 

 and also the young state in the Ispoda. 



Thanks to Professor Owen, I am now in a position to rebut Vander Hoeven's and 

 Dr. Dohrn's arguments as to the presence of only one pair of anterior extremities 

 supplied with nerves from the supraoesophageal ganglion, and to show by the admirable 

 series of dissections of the nerves drawn on Pis. XXXIV, XXXV, and XXXVI (repro- 

 duced from Professor Owen's Monograph), that, as in other Crustacea, Limulus possesses 

 two distinct pairs of appendages (antennules and antennae) which derive their neuration 

 from two pairs of nerves arising from the front of the supraoesophageal ganglion. Van 

 der Hoeven's statement must therefore be considered as incorrect. 



He further confirms the statement made by me (' Quart. Journ. Geol. Soc.,' 1866, 

 vol. xxiii, p. 33), that the thoracic or opercular plate derives its innervation from a 

 cephalic ganglion, whereas the succeeding inner posterior branchigerous plates are 

 appendages of the thoracic somites. 



Concerning the Eurypterida, so far as our present knowledge extends, I must 

 adhere to my already published conclusion, namely, that one pair of antennary organs is 

 suppressed 1 — a strong argument in favour of the theory of the retention of larval 

 characters by these palaeozoic forms. 



With regard to the under lip (metastoma), it seems singular to base the refusal of a 

 place to Limulus among the Crustacea upon the fact that the metastoma is rudimentary, 

 whereas in Pterggotus it is very large, formed in one piece, having a ridge in the mesial 



1 According to Spencc Bate and Fritz Miiller the second pair of antennae are absent in the females of 

 Brachyscelus, although the male possesses them like other Amphipods. 



