g6 PHYLOGENY OF FUSUS AND ITS ALLIES. 



mens show a strongly Urate outer lip, a strong posterior canal, a pro- 

 nounced transverse plication on the columella, just below the canal, 

 and usually a faint oblique grove on the columella. 



Localities: The localities given by Basterot for this species are 

 Leognan, Saucats, and Merignac, France. In the following list the 

 numbers refer to the collections of the Museum of Comparative Zoology. 



Var. tiibcrculosiis Leognan (M. C. Z. 1321) ; Dept. Landes (M. 

 C. Z. 1323) ; Castel Arquato ( ?)* (M. C. Z. 1324) ; Cabannes-St. Paul, 

 Dax (1329) ; Leognan et Saucats (27802). 



Var. carinatus Bordeaux (1315, 1316) ; Paris Basin (?)* (1317, 

 1318) ; Leognan et Saucats (1319). 



Typical form: Leognan et Saucats (1320, gerontic, 27801) ; Bord- 

 eaux (27803, 27804, also young 1322, accelerated, 1314). 



Var. major: Steenabrunn, Vienna Basin (1327, 1328) ; Leognan et 

 Saucats (27800). 



Besides the varieties given above, the following have been named 

 by Grateloup : var. scahra, contorta, aspera, calcarata, plicata, dubia. 



Horizon: Miocene. 



C. PHYLOGERONTIC FUSID^. 

 15. THE GENUS CYRTULUS Hinds. 



(1843. Hinds, Ann. and Mag. Nat. Hist., vol. XI, p. 256.) 



This genus was made by Hinds for the reception of a remarkable 

 gastropod shell found in the Pacific Islands. In its young stages this 

 species is a typical Fiisns, and might be classed with the coIks series, 

 with the species of which it agrees in all its general characteristics. 

 The adult whorls, however, show a remarkable deviation from this 

 slender Fusoid growth, consisting of thick irregular whorls, loosely 

 wrapped about one another with a complete loss of shoulder, spirals, 

 ribs and other surface features, and with a complete obliteration of the 

 characteristic form of the young. 



This type of structure, which may be designated melongenoid, 

 from its characteristic occurrence in Melongcna melongcna and related 

 species, is essentially an accentuated development of old age char- 

 acteristics of the type found in normal Fusi in senescent individuals. 

 In the present type it has become an established characteristic and from 

 a gerontic feature has been pushed back to the ephebic and even 

 the late neanic stage through the operation of the law of acceleration. 

 Species of this genus, then, must be considered as phylogerontic Fusi, 

 i. e., species which are typical Fusi when young, but when adult are 

 characterized by structural features found only in extreme old age 

 individuals of the normal Fiisiis series. 



It has become customary to unite this genus with the Eocene genus 

 Clavilithes described earlier by Swainson. These two genera have, 



* Probably an error. 



