Reports and Proceedings. 491 



from the shell of a Mollusk, which, is, after all, only the protective 

 sheath, and not the animal itself, rests on very uncertain grounds. 



The shells of the Palaeozoic Cephalopoda may in some instances 

 have been internal, and in others external, and the animals to which 

 they belonged were perhaps widely separated zoologically. Nor is 

 the simplicity or complexity of the shell a sure proof of its relative 

 zoological position. The many-chambered shells of Spirula and the 

 simple shell of Argonauta, both belong to the Dibranchiata, yet how 

 widely different in structure. Some of the Palseozoic forms of shell, 

 such as Trochoceras, Phragmoceras, Gomphoceras, Ascoceras, etc., may 

 have been the internal shells of early Dibranchiates, qui sait ? 



Taking the Cephalopoda as a whole (not looking at Silurian forms 

 alone), there can be no doubt of the concordance between the zoo- 

 logical and chronological records. For the later and higher forms 

 are not the many-chambered Tetrabranchiata (represented in palaeo- 

 zoic times by the Orthoceratidae, etc., and at the present day by the 

 pearly Nautilus), but the active internal-shelled Dibranchiata, the 

 Squids and Cuttlefishes, whose advent takes place in Neozoic times, 

 long after the reign of Orthoceras had passed away. 



In venturing thus to differ from so illustrious a Paleontologist as 

 M. Barrande, we would not for a moment have it inferred that we 

 desire in the least to disparage his grand work on the Cephalopoda 

 of Bohemia, which, with his labours on the Trilobites of the same 

 country, will remain the most lasting monument of his genius and 

 industry ; but we merely suggest that^the results of future research 

 may induce M. Barrande to alter his views on the question of evolution. 

 H.W. 



The Development of the "King-Cbab," Limulus polyphmmxis. 



By A. S. Packard, Jun., M.D., Salem, Mass., U.S.A. 

 [Read before the American Association for the Advancement of Science. Communi- 

 cated by Prof. C. H. Hitchcock, State Geologist of New Hampshire]. 



The following were the chief conclusions of the Author : — 



THE eggs of Limulus are laid in great numbers loose in the sand, 

 the male fertilizing them after they are deposited.^ This is an 

 exception to the general mode of oviposition in Crustacea ; Squilla 

 being the only other genus in which the eggs are not borne by the 

 female until maturity.^ 



Besides the structureless dense irregularly laminated chorion 

 there is an inner egg-membrane composed of rudely hexagonal cells. 



1 In the' higher Crustacea the eggs appear to be impregnated by the male before 

 they leave the ovaries. — Edit. Geol. Mag. 



2 Another exception is the Land-Crab of the West Indies, Gecarcinus ruricola, 

 which is said to leave its home in the highlands of Jamaica, when the spawning 

 season arrives, and march in a direct line towards the sea-shore for the purpose of 

 depositing their eggs in the sand, the young Gecarcini being marine-dwellers until 

 they have undergone their larval metamorphoses. Professor Bell, in his History of 

 the " British Stalk-eyed Crustacea," p. 79, says, of the common Shore-crab {Garcinus 

 McBnas), "Like most of the Brachyura, this species buries its ova in the sand." 



