612 



THE AMERICAN NATURALIST 



[Vol. XLI 



ing of the whorl are generally accornpanied by the loss, or at least 

 a modification, of the ornamentation. 



A second important type of modification of form in ontogeny 

 is the angulation of the whorls. This begins as a slight depression 



angulation ajjpears in the ambital portion of the wliorl/which 

 usually occurs where tlie whorl is marked by the first or most 

 pronounced of the spirals. From a faint beginning, the anjrle 



and body surface incrcnscs. until the whorl consisls of two pcM-iVctly 

 Hat or ™ slighdy concasc surface srparaird In a sharp a.i.uh' 

 (Fig. 2). Where the uiignlation appears lalf in the oulogmy, 

 generally about an e(pial Hat space is shown al)()\(> and below the 

 angle (Fig. 8). When it appears early, th(> later whorls gvnerally 

 embrace the preceding more strongly, thus decreasing the space 

 below the angle, until in extreme cases this lower space has entirely 

 disappeared, the suture of the succeeding whoii being at the angle 

 (compare Fig. 5 with the younger ])ortion of another individual 

 enlarged in Fig. 2). This i)roduces a continuous slope of the spire, 



Conus, where thV shoulder makes a right angle with the axis of coil- 

 ing of the shell, to nearly vertical as in some 'riirrilellas and Ceri- 

 thium, where tlu- shonhler makes a very acute angle with the axis 



less closely coiled, so that in the w.iing spin- th(> (lattened bodv 

 of the wiiorl, below the angnlat'ioti, b(>conics xisible (Fig. 2). 



round-whorled con 



