112 AMERICAN JOURNAL 



however, I am able to state, from examination of the typical 

 specimen, is a very different shell, and probably belongs to another 

 genus. It is certainly not an Amycla. The animal of A. 

 versicolor is white, with black dots and streaks. The teeth, as 

 figured, are typically Columbelloid. 



The terms applied to opercula are so very indefinite, that two 

 authors may intend the same thing by different names, or different 

 things by the same name. A few words of explanation may not. 

 be out of place. 



A buccinoid operculum, as I term it, is one after the type of 

 the operculum of Buccinum undatum, in which the nucleus is 

 simple, close to the outer margin, which is convexly arcuate, but 

 usually a very little inside the margin, which increases by regular 

 concentric lines of growth toward the inner side, and which is 

 provided on the inner surface with a smooth polished callosity, 

 which borders the outer, and, to a gi eater or less extent, the 

 entire margin. Some species have a subcentral nucleus. 



The operculum of Amphissa differs from this only in having a 

 straight spur of callus extended toward the centre of the oper- 

 culum. The operculum of Nitidella Goiddii is of similar con- 

 struction. The nucleus is close to the outer margin, but in 

 perfect specimens of Amphissa it is not quite marginal.* In 

 imperfect or worn specimens it is often marginal, or even worn 

 off entirely. This kind of operculum may, for distinctness, be 

 called amphissoid. 



A purpuroid operculum, on the other hand, is often externally 

 similar to the one above described, but on the internal surface it 

 is quite different and characteristic. The nucleus is within the 

 margin, and the outer border is covered with a thick callus. 

 The nucleus is, however, surrounded with peculiar lines of in- 

 crease, concentric, but irregular, as if the operculum had rotated 

 at different periods of its growth, with relation to the aperture 

 of the shell. This form of operculum is seen in Purpura patula 

 and P. lapillas, and is quite different from that of Nitidella 

 G-oiddii, which Dr. C arpenter calls Purpuroid. 



A nassoid operculum, as I regard it, is subquadranguhir with- 

 out a very distinct nucleus, notched on the upper and lower 

 edges, smooth and sharp on the outer and inner edges, and in- 

 creasing by additions to its inner edge, with a border of callus 

 on the other three sides, when perfect. Such is the operculum 

 of Nassa Icevis, figured by the Messrs. Adams, differing totally 

 again from the operculum of "Amycla," (= Astyris + A»tphissa) y 

 described as nassoid by Carpenter, though probably like the 



* In Nitidella cnbraria and Astyris carinata it is subcentral. 



