PlIVLOGENY OF FUSUS AND ITS ALfJES. 



97 



however, no genetic relation whatever, belonging to entirely distinct 

 families of gastropods, and having only an external resemblance in 

 their respective adult stages. This resemblance is often very close 

 when the adult stages arc alone considered, but the great differences 

 are at once shown when the young are examined. This resemblance is 

 simply a case of parallelism, in which features of the same type recur 

 in corresponding stages of otherwise entirely distinct individuals. This 

 is a case similar to the noncoiling of the Cretacic Ammonoids, where 

 this feature recurred in a number of phylogerontic individuals be- 

 longing to entirely distinct genetic series. To class Cyrtulns and 

 ClavilitJics together is as great a mistake as to unite the genera 

 Macroscaphitcs and Ancyloccros under the same generic name, simply 

 because they are both partly uncoiled Ammonoids. 



CYRTULUS SEROTINUS Hinds. 



1843. Cyrtulns scroliniis Hinds, Ann. .Mat^. Nat. Hisl., vol. XI, p. 257. 



1844. Cyrhtliis scnUiiius Hinds, Zool. Voy. H. AT. S. Sulphur, vol. 2, p. 13, pi. 

 I, figs. 12, 13. 



The protoconch of this species has been fully preserved on only 



one of the specimens seen (Am. Mus. Nat. Hist.), though another 



specimen (Nat. Mus. 91755) and several others in the American 



Museum show the last portion. It is prominently developed, consisting 



Figs. 13 and 14. Cyrtulns serotinus. Coll. Bost. Soc. Nat. Hist.. 27S. 



of nearly two and a half volutions. It ends abruptly with a varix. and 

 the normal round-whorled and ribbed type of Fusits conch begins as 

 abruptly ; the last whorl and a quarter of the protoconch are finely 

 ribbed verticall}- as in Piisiis. with which this portion agrees perfectly. 



