PIIYLOGENY OF FUSUS AND ITS ALLIES, 9 



(F. longirostris) in which it consists of as many as two volutions.* 

 The first whorl is smooth, obhquely erect, and rather prominent, the 

 apical end convex and large. The diameter just below the apex is 

 but slightly less than that at the end of the first volution. The en- 

 largement of the remaining portion of the protoconch is also very 

 slight, the shell thus having the appearance of having a swollen or 

 apical whorl. The last half of the protoconch is marked by fine 

 vertical riblets, which are either closely crowded or separated by inter- 

 spaces having from two to three times the width of the riblets. In 

 rare cases are the interspaces, and still more rarely the riblets marked 

 by visible revolving lines or " spirals," though such lines of excessive 

 tenuity and visible only in the young shell may be present. 



The protoconch generally ends abruptly with a varyx, w^hich some- 

 times is a riblet scarcely more prominent than the other riblets on the 

 protoconch, or again is a strong rounded vertical ridge, two or three 

 times the width of the normal riblets of the protoconch. The orna- 

 mentation of the nepionic shell begins abruptly, commonly in the form 

 of spirals and rounded vertical ribs. 



These peculiarities of the protoconch of Fiisus stamp this genus 

 as a remarkably accelerated type. Ordinarily in gastropods no orna- 

 mentation is shown on the protoconch, though Fusns is by no means 

 the only one in which it occurs. Some of the other genera with 

 ornamented protoconch will be mentioned below, but so far as my 

 observations extend, the number of genera with such markedly dif- 

 ferentiated protoconchs is comparatively few. In Falsifusus and 

 in many species commonly referred to Latirus, Pleurotomaria and 

 other related genera, the apical end is highly ornamented in the later 

 stages, but this ornamented portion merges into what is clearly a 

 portion of the shell itself. It is therefore somewhat doubtful whether 

 the ornamented subapical whorls of these shells are a part of the 

 protoconch or whether they represent a part of the nepionic shell. 

 The same is true of other shells, in which the ornamented portion im- 

 mediately succeeding the smooth portion may represent the nepionic 

 shell instead of the protoconch. In Fusits, however, the protoconch 

 ends abruptly, there being a sharp line of demarkation between the 

 two, and the junction is furthermore accentuated by the development 

 in most cases, of a distinct varix. Similar characteristics occur in 

 Hemifusus, the ribbed portion of the protoconch being in this genus 

 extended, so as to complete two volutions.t 



*The term volution is employed throughout this paper to denote a com- 

 plete revolution of the shell, the beginning and termination of the volution bcmg 

 in the same line, the one above the other. The term whorl is used in a less 

 precise manner, being employed as it usually is in conchology, 

 t Grabau, Am. Nat., vol. XXXVI, p. 921, fig- 5- 



