240 INVERTEBRATA OF MASSACHUSETTS. 



Of the five specimens I have examined, three were mature, and two 

 young. In the oldest, the width of the shell is proportionally greater, 

 and there is a tendency to angularity at about the upper fourth of the 

 last whorl. 



Genus JANTHINA, Lam. 



Shell sub-globose, thin, fragile, spire short ; aperture angular 

 at the anterior junction of the inner and outer lips ; pillar twisted ; 

 lip thin, loith a sinus at the middle. 



JAnthina frAgilis. 



Shell thin, brittle, conical, ventricose, violaceous beneath, whiter 

 on the spire. 



State Coll., No. 292. See. Cab., No. 942. 



Helix janthina, Lin.; Gmelin ; Syst., 3C45, No. 103. Lister; Conch., t. 572, 

 f. 24. RuBiPHius; Mus., t. 20, f. 2. Gualt. ; Test., t. G4, f. O. Sloane ; 

 Jaynaica, t. 1, f. 4. Brown; Jamaica, t. 3d, f. 2. D'Argenv. ; Conch., pi. 6, 

 f. 5. Chemn. ; Conch., v. t. IGG, f. 1.377, 1578. Wood ; Index, pi. 34, t. 116. 



Janthina fragilis, Brug. ; Encijc. Mith , pi. 456, f. 1. Ann. du Mus., xi. 123 

 (animal). Blainv. ; MalacoL, pi. 37 bis., f. 1 a. Sowerby ; Couch. Man.., 

 f. 333. 



Janthina communis, Laji. ; Jin. sans Vert., (1st. ed.) vi. 206. 



Shell globose-conic, thin, brittle, transparent ; whorls three or 

 four, forming a short spire, the last one very large, and angular at 

 the middle ; beneath the angle the color is deep violet, lighter 

 about the axis, and above it the color is merely tinted with violet, 

 a little darker at the suture ; surface shining, wrinkled by the lines 

 of growth, and with short, oblique wrinkles above the angle of 

 the last whorl, and marked with revolving lines beneath that angle ; 

 aperture large, semi-oval, outer lip very thin, retiring as it passes 

 the angle of the whorl, so as to produce a shallow recess ; inner 

 lip cylindrical, straight, corresponding with the axis of the shell. 

 Length y^g inch, breadth 1 inch. 



The Janthina floats, by means of a mass of vesicles, at the 

 surface, throughout the wide ocean, and is not unfrequently driven 

 upon the ocean shores by storms. After a severe gale, in the 



