No. 432.] STUDIES OF GASTROPODA. 941 
them, — namely, Hemifusus (Melongena) morio. Representa- 
tives of this species occur in both west African and West 
Indian waters. From the west African type appears to have 
been derived the Mazatlan species Melongena patula, while M. 
melongena, at home in West Indian waters, was derived from 
the West Indian representative of H. (M.) morio. In both 
species the phylogerontic melongenoid form of whorl appears 
immediately after the tubercled and before the spinous stage, 
this latter coming in somewhat later. Thus, while the mode of 
coiling has become senile, the formation of the spines indicates 










A ‘oe 9 ] 
sant 20 | 
Je hl oh | 2}, $ 
rashes | av ce od l 
C 1 us M 9 | € | A J 
ic-] 2c oc l Coie | 
N 1 ac E: 94 l 33 | 4A | z4 ] 
L7 i07] eu od T au ij — | 
E Ride ee | 9 I " | E 1 e l 
te- 4e -T ve T 4c | siu 3 oT I 
F 1ta nes! of J AT i =e | E I me 1 
dip 217] ol Í a EET F o1 j] OF ge ia 1 
G 1 Pere d o9 l D oy. 1 Ac |x Le | To x J 
ig tee «4 PET 1 ig | 
H 7e que ot) DI ] Ah l Th TIDES | 
in-T-2n-7T T Ah T ih i 
I E11 E 91 ] 9 ER US S. As | T: SS ml 
a4 | al ! ol i 41 | ai Í ol | 
Fic, 16. — Diagram a Hyatt’s Law of Serm in Development. 
or description see tex 
the persistence of one portion of the vigor of the adult. 
Such form of acceleration may be called partial or incomplete, 
differing in that respect from Fulgur, in which the acceletation 
is complete. A reason for this may perhaps be found in 
the following consideration: Fulgur is an accelerated type. 
in the present fauna. The species in which a separation 
existed between the tubercles and spines all lived in Miocene 
and Pliocene times, and hence in the modern descendant (F. 
carica) spines have become firmly established. We may further 
suppose that the power to form spines has persisted so long 
that in the adult it is on the wane; and hence if any phylo- 
gerontic types of Fulgur should arise, the spines would first 
disappear and probably would never be formed again. In 
Hemifusus, on the other hand, the spine-forming power has 
