No. 432.] STUDIES OF GASTROPODA. 923 
conch features closely similar to those of Fusus, and the con- 
sideration of these alone has caused them to be placed in that 
genus. (Compare Fig. 6.) These examples, however, are due 
to parallelism rather than close genetic relationships. Great 
similarity exists between the protoconchs of Fusus and Hemi- 
fusus, thus showing a close genetic relationship between these 
two genera, while on the other hand Fasciolaria appears to be 
more widely removed. 
Septa in the Apex of Gastropods. — Gastropoda in which the 
spire of the shell is long, generally develop septa near the apex. 
These septa partition off the protoconch and earliest whorls of 
the conch, and they may generally be seen 
in specimens with broken apices. Turri- 
tella, Cerithium and its allies, Fusus, and 
in fact turreted shells in general show this 
septum. It is generally a curved, more or 
less funnel-shaped element, though often 
only meniscus-shaped. The septum is invari- 
ably convex backward, as might of course be 
expected. The apical portion is generally 
uniformly curved and lies freely in the cav- 
ity of the protoconch or early conch. Septa , 6 — Fuss asper Sow 
are sometimes very numerous as observ- Atypical primitive Fusus. 
able in longitudinal sections (Triton, etc.), Kowss, Paget. ~ ıb 
but generally the number is comparatively smal]. The septa 
are entirely imperforate and mark the withdrawal of the apical 
portion of the coiled visceral hump from the apex of the shell 
and the cutting off of the useless space by a partition wall. 
In a number of types the portion of the shell thus divided 
off becomes invariably broken away. An interesting type of 
structure which belongs here is found in the recent Scaphella 
magellanica Sby. and some related forms. In this, according 
to Dall,! « the larva is clothed with a cuticular or horny proto- 
conch, probably similar in form to that which when shelly 
results in the ‘bulbous nucleus.’ Later on, but while still in 

1 Dall, W. H. Blake Gastropoda, Bull. Mus. Comp. Zool, vol. xviii (1889), 
P- 452; Proc. U.S. Nat. Mus., vol. xii (1890), p. 311, Pl. IX, 6; Trans. 
Wagner Free Inst. of Sciences, vol. iii (1890), p. 67, Pl. VI, Fig. 5- 
