66 PROCEEDINGS OF THE ACADEMY OF [1890. 



ON THE MODIFICATIONS OF THE APEX IN MUREX. 

 BY FRANK C. BAKER, 



The embryonic apex in this group consists of from one to one and 

 a quarter (in one instance of two and a half), polished, unvarixed 

 whorls, which are either rounded or carinated, and are generally 

 provided with a distinct varix at the ending of the embryonic whorl. 

 The tip of the apex is in many of the species a little depressed and 

 bent down on one side, and the top of the embryonic whorl is, with 

 one exception, that of Murex scolopax Dillw., always rounded. The 

 embryonic whoi'l is in some species sharply carinated, in others 

 rounded with a thread-like carina, and in not a few it is simply 

 rounded. The varix at the ending of the embryonic whorl, may be 

 either triangular, rounded, large or scarcely visible ; the presence of 

 this varix indicates, without doubt, the point where the shell began 

 its independent existence after leaving the egg. 



The carina, Avheu present, begins about midway of the whorl, and 

 after traversing the whorl in an oblique direction finally terminates 

 in the suture above the whorl below, or is continued in the lowest 

 spiral thread of the succeeding whorl. The whorls succeeding the 

 embryonic are generally rounded and provided with from nine to 

 thirteen small, rounded longitudinal ribs, which in turn are usually 

 crossed by four fine spiral threads. 



In comparing specimens with the following descriptions, they 

 should be held with the varix of the embryonic Avhorl toward the 

 left hand. The aperture of the shell is no guide, inasmuch as each 

 turn of the shell brings the apex in a different position. 



In the present communication I have restricted my observations 

 to the typical Mxirex, or Trihulus group. 



The only author who has described the apices of Murex, so far as 

 known to me, is Watson, who, in the Report on Gasteropoda of the 

 Challenger Expedition, has given valuable remarks on several of the 

 species treated below, as well as some others. 



Genus MUREX Linn. 



Subgenus MUREX (Sensu stricto). 



Murex scolopax, Dillw. (Fig. 1). 



The embryonic nucleus consists of two smooth, glossy fulvous 

 whorls, of which the second is twice as large as the first ; a carina 



