1874.] 225 [Hyatt. 



but that great internal changes had also to be accounted for, inas- 

 much as Chologaster had a much longer intestine, with an additional 

 turn, than either Typhliehthys or Amblyopsis, and had a stomach 

 provided with two pairs of pyloric appendages, while the other gen- 

 era had but one pair, and had the single ovary placed behind the 

 stomach in the posterior part of the abdominal cavity, whereas in 

 the other two genera it was situated at the side of the stomach, and 

 in the forward part of the cavity. With such marked differences as 

 these to be taken into consideration, he thought it would be rather 

 hasty for any one to assume that one genus was developed, in the 

 ordinary acceptance of the term, from the other ; and that with all 

 the facts we now have, it was assuming more than the facts war- 

 rant, to accept as truths any of the arguments that have been 

 brought forward so far as they relate to the origin of the blind 

 fishes ; and he thought that there were as many, if not more, facts 

 in favor of their having been a very early form of life that had 

 been continued, than one of late development ; and if it could be 

 shown geologically that marine life had once had access to the first 

 formed of these caves in any way, he thought that many of the facts 

 would be as well understood on the basis of the continuance of types 

 from past time, as upon that of their late evolution. 



Remarks on two New Genera of Ammonites, Agassiceras 



AND OXYNOTICERAS. By PROF. A. HYATT. 1 



Family ARIETIDJE. 



AGASSICERAS. 



The young are quite immature and remarkable for the prolonged 

 existence of the goniatitic form which is generally confined to the earli- 

 est stage of growth in the Ammonites. The living chambers are quite 

 short, the abdomen keeled but not channeled. This genus would not 

 be placed in the group of Arietidae by many authors. A comparison 

 of the adult with the perfect young of A . obtusus, which I saw in the 



1 1 am now publishing so many of these fugitive papers that I feel called upon, 

 tn advance of a more formal Memoir now in manuscript, which is to appear in 

 the Bulletin of the Museum of Comparative Zoology at Cambridge, to thank my 

 many friends in Europe, to whom I have been indebted for much information 

 and the free use of collections. To mention any one by name would be unjust to 

 others, and I therefore defer more formal acknowledgement until the appearance 

 of the Memoir referred to. 



PROCEEDINGS B. S. N. H. — VOL. XVII. 15 FEBRUARY, 1875. 



