54 PEOCEEDINGS OF THE GEOLOGICAL SOCIETY, [DeC. 20, 



to the cephalothorax* ; and the abdominal spine is prominent, being 

 ensiform and about three times as long as broad." 



V2tli stage. — "At this, and also in the second or succeeding moult, 

 which occurs about four weeks after the first, the young Limulus 

 doubles in size." 



I now beg leave to say a few words as to the conclusions arrived 

 at by these authors. 



Of the Kev. Dr. Lockwood's paper, it may be remarked that his 

 acute observations as to the Hkeness of the Limulus-emhrjo to 

 young Trilobites and also to Pterygotus and Eurypterus, are those of 

 a man who catches at the main features of any form of structure, 

 and at once is able to call to mind a comparison, although not always^ 

 the correct one. His remarks are, however, of great value, and' 

 many of his figures of the young of Limulus are of much interest. 



His comparison of the posterior shield, composed of the thoracico- 

 abdominal segments, with the"telson" or " pygidium " of PiJsry- 

 gotus shows that he has not ascertained their relation to the rest of 

 the structure of the animals so compared. 



Dr. Packard, after referring to the dense chorion of the egg 

 in Limulus, which splits and is thrown ofi^ during the develop- 

 ment of the embryo within the inner egg-membranfe (" amnion " 

 or " blastoderm," Packard), observes that the primitive band, unlike 

 that of the Crustacea generally, is confined to a minute area, and 

 rests upon the top of the yelk, as in the spiders and scorpions 

 and certain Crustacea (namely, EripMa spinifrons and Astacus jiu- 

 viatilis, Palcemon aclspersus and Crangon maculosus), in Vvhich there 

 is no metamorphosis. 



" The embryo," says Dr. Packard, " is a Nauplius ; it sheds its 

 Nauplius-skin about the middle of its embryonic hfe. This Nau- 

 plius-skin corresponds," he considers, " in some respects to the ' lar- 

 val skin ' of German embryologists." But he adds, " the recently 

 hatched young Limulus can scarcely be considered a Nauplius (like 

 the larvse of the Phyllopoda), but is to be compared to those of 

 the Trilobites " (e. g. Trinudeus ornatus, Sao hirsuta, and Agnostxis 

 nudus), which, in the youngest condition observed by Barrande, 

 have only the head and pygidium, the thoracic segments being 

 added at subsequent moults. Dr. Packard thinks that the cir- 

 cular larva of Sao hirsuta approaches nearest to the JSFauplius-form 

 of the Phyllopods, though he contends that it is not a Nauplius. 



He adds, " the larva passes through a slightly marked metamor- 

 phosis. It differs from the adult simply in possessing a less number 

 of abdominal feet [thoracic branchiferous feet, H.W.] and in having 

 only a rudimentary spine." 



"Previously to hatching, it strikingly resembles Trinudeus and 

 other Trilobites, suggesting that the two groups should, on em- 

 bryonic and structural grounds, be included in the same order, 

 especially now that Mr. E. Billings has demonstrated that Asaphus 

 possessed eight pairs of five-jointed legs of uniform size." 



[I shall presently take occasion to show the inconsequence 

 * Cephalic plate. — H. W. 



