50 ERIC -n ; 



Mr. Alpheiis Hyatt has remarked that the young of all the 

 coiled cephalopods start \vitli :i straight or bent cone. and beu'in 

 their coil abruptly, always leaving an opening in the umbilicus 

 through the centre of the iirst whorl. The development of the 

 Nautiloids, in time, is also marked by a gradual involution from 

 the perfectly straight Orthoceras to the A"'////////s I'mn/iilinx, 

 where the expansion of the last whorl conce:ils the umbilicus. 

 Tlu' progress of the Ammonoids. on the other hand, is marked 

 by the gradual uncoiling of the shell, ending with the straight 

 Kaculites of the cretaceous; this feature is. iherefore. of great 

 importance in a natural classification of these groups.* 



Mr. Hyatt has also carefully studied the embryology of tin- 

 shell of the fossil cephalopoda; and in a richly illustrated 

 memoir, published by the Museum of ( Comparative /oology, at. 

 Cambridge, Mass., he attempts to prove the development theory 

 by the results of these studies. 



M. Joachim IJarrande, however, who is the most distinguished 

 of living authorities upon the fossil eephalopods. differs in toto 

 from Mr. Hyatt's,decisions. He has published (in 1*77) Ktudes 

 Ge'nerales," in which he devotes over two hundred octavo p 

 to a careful review of the entire subject, and reaches the follow- 

 ing conclusions : 



I. (irncrir 7///">-. 



1. Absence of cephalopoda in the primordial silurian fauna of 

 all the countries where it has been ascertained to exist ; that 

 is to say in about 25 natural basins, largely spread over the 

 two continents. This absence- is in harmony with that of the 

 acephala and the rarity of gasteropoda and heteropoda in 

 the same fauna. It is Inexplicable by tin- theories of evolution. 



2. Sudden appearance of 1 '2 types of eephalopods in the first 

 aspect of the second Silurian fauna. 



This sudden appearance is as inexplicable as their total 

 absence in the primordial fauna. This number. ]-2, consti- 

 tutes nearly half of the "2(\ types admitted in his studies. 

 among the ."> families: Xautilida-. A sroeerat ida- anddonia- 

 tida-. 



* /'roc. Bost. 8oc. N. I/., til, '-.'Hi, 1868. 



