358 PROCEEDINGS OF THE ACADEMY OF [Mav, 



have been subjected to breakage, often exhibit a sudden and sharp 

 development of senile features. The shell gets heavy, the growth lines 

 become irregular, and the spines tend to pass into a shoulder keel. 



An individual of Ecphora quadricostata, collected by the writer from 

 the Maryland Miocene, exhibits acceleration produced by accident 

 very clearly. The accident occurred to the shell during the develop- 

 ment of the third whorl. From this point on the rate of the develop- 

 ment of later shell features increases, and is much more rapid than in 

 normal individuals. The individual in question never became mature, 

 only attaining five whorls. A normal specimen with this number of 

 whorls has practically no indication of loose coiling in the region of the 

 colimiella, and the spiral folds are simple. The abnormal individual 

 in question shows plainly a loose coiling in the columella region, and 

 the spiral folds approximate those of more mature individuals. Toose 

 coiling is, as a rule, not marked in normal individuals of this species 

 imtil the seventh or eighth whorl. 



A specimen of Fulgur canaliculatwn collected at Longport, New 

 Jersey, exhibits well the acceleration of characters produced by break- 

 age in the shell. ^^ In the canaliculate Fulgurs the transversely ril^bed 

 condition occurs very early, and is followed by a few angular whorls, 

 bearing tubercles on the shoulder angle. These tubercles soon pass 

 into a shoulder keel, and this in turn disappears, and leaves the whorl 

 rounded, in the more accelerated forms, such as Fulgur pyrum. 



Fulgur canaliculatum, however, never entirely loses the shoulder keel, 

 which marks its last stage of development. In the specimen under 

 consideration the accident occurred when the shell was young, on an 

 angular whorl having the tubercles so characteristic of the early stages 

 of Fulgur canaliculatum. After the break the shoulder angle is not 

 reproduced, but the whorls continue to the aperture of a shape much 

 as in Fulgur pyrum. Just after the break there is, apparently, an 

 attempt to reproduce the tubercles on the rounded surface of the whorl. 

 This attempt was, however, unsuccessful, and the whorl continued 

 smooth. An examination of the soft parts showed the specimen to 

 be identical with normal male individuals of the species, except that 

 the shoulder angle is not present on the mantle. No peculiarity in the 

 mantle edge or other soft parts could be detected which would account 

 for the change in shell ornamentation. 



The acceleration in this case has caused the dropping out of that 

 marked character of the later whorls of the species, namely, the un- 



" Smith, Burnett, Proc. Acad. Nat. Sci. Phila., June, 1902. 



