
920 THE AMERICAN NATURALIST. [Vor. XXXVI. 
of whorls which increase slightly or not at all in size, thus giving 
a long and slender type of protoconch which Dall has called 
*pupiform." This type of protoconch is characteristic of 
Clavilithes of the Paris Eocene (Fig. 2), of many Eocene and 
recent species of Turbinella, and of other forms. 
The trochoid type of protoconch is apparently a case of 
specialization, and is confined to a comparatively small number 
of gastropods. 
The naticoid initial whorl of the protoconch, so far as has 
been observed is umbilicated. This is well shown in Fulgur, 

Fie. 4. TE canaliculatus in the phylembryonic stage. a h, heart ; mo, mouth; 
eye; sh, shell (protoconch); ž, tentacle. x 3 
Sycotypus, Fasciolaria, Buccinum, and other types in which 
the initial whorls are large enough to be readily examined. 
The umbilicus is best shown in young individuals which have 
just completed the early protoconch stage (Fig. 3). It is well 
marked in Fulgur at the end of the protoconch (phylembryonic) 
stage, before the velum is fully developed (Fig. 4). This latter 
persists until just before the animal leaves the egg capsule, by 
which time the young conch has begun to develop and the 
umbilicus is closed. I believe that we are warranted in assum- 
ing that the umbilicus exists at some stage in the protoconch 
of the majority of gastropods, though it is conceivable that in 
extremely accelerated types, even this — apparently the most 
