WOOD, PHYLOGENY OF CERTAIN CERITHIIDM 73 



adult condition is reached. The ornamentation of the adult consists of 

 three rows of nodes of which the upper are larger and more widely spaced 

 than the others, and the nodes of the median row are very fine. An 

 irregularly nodose fine spiral is barely visible just above the suture. The 

 body volution has two strong spirals below those already mentioned. On 

 this volution the growth lines become very much crowded, and all the 

 nodes become indistinct, especially toward the later part of the volution. 

 The aperture is about equal in length and breadth and is roughly quad- 

 rangular in outline. The callus of the inner lip is broad and thin. The 

 siphonal canal is short, widely open and somewhat twisted. The outer 

 lip is thin and has a strongly sinuous outline. 



HoKizoN AND locality: Sables Moyens superieur (Upper Eocenic). La 

 €bapelle, Paris Basin. 



No. 20149, Columbia University collection. 



Eemarks : The ornamentation of this species closely resembles that of 

 P. tuberculosa, both in its development and in the adult stage. The 

 species differs from P. tuberculosa in its smaller size; narrower apical 

 angle, which makes it a more slender shell; its shorter canal and more 

 angular aperture. 



This species bears the same relation to P. tricarinata as does P. tubercu- 

 losa — that is, it is derived from the same ancestor as both, but develops 

 in the direction of P. tuberculosa, to which it is closely related. 



Potamidopsis crassinoda sp. nov. 



Measurements : Lengtb of specimen with apical whorls missing, 39.8 mm. ; 

 greatest diameter, 26.7 mm. ; apical angle, 32°, changing to 23.8° on the sixth 

 volution ; sutural angle, 85°. 



This species is distinguished from Potamidopsis tuberculosa, to which 

 it is closely related, in being a larger and thicker shell and in having the 

 nodes of the surface much larger and more prominent. This difference 

 begins at an early stage of growth and continues throughout the life of 

 the animal. The youngest volution preserved is 2.5 mm. in diameter, 

 and several whorls have evidently been broken away above this. The 

 first three volutions have an ornamentation of about the same strength 

 and character as the adult of P. tuberculosa, but beyond this the large 

 nodes characteristic of all the later volutions are developed. The nodes 

 of the uppermost row are large, lilunt cones ; those of the lowest row, 

 smaller and transversely elongate. The median nodes are very fine and 

 on some specimens nearly obsolete. The base of the volution is produced 

 into lobes, which sometimes overhang the succeeding volution. 



