208 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.54. 



in actual size but in the length of the coil of whorls and the size 

 and compactness of the larval apex. 



The most common and typical nucleus comprises one or two 

 whorls of a thin, smooth, more or less inflated character, while this 

 normal sculpture of the adult shell usually commences abruptly at 

 the termination of the nuclear coil. In some cases there are three or 

 more nuclear whorls Avhich are then usually coiled in a subcylindri- 

 cal fashion. 



The apex or initial whorl of the first fundamental type may pre- 

 sent either of the following phases: (1) a bulbous appearance at 

 times even larger in diameter than the next succeeding whorl; it 

 may, however, be (2) small and coiled upon itself in a regular man- 

 ner, gradually increasing in size. It may be (3) tilted obliquely to 

 the axes of the succeeding whorls, or it may be (4) so compactlj- 

 coiled that the initial cell forms with its first half whorl a little angle 

 or point which forms the actual apex of the spire. Again the initial 

 cell may be (5) quite small and regularly increase, with a low blunt 

 spire recalling the appearance of a small Turho viewed vertically 

 from above. Most of these mutations are incidents of growth, and 

 while the nucleus in a general way remains tolerably constant in 

 form (though varying in size) within the species, I have found cases 

 where from the same bunch of capsules one might select bulbous 

 turbinoid, or laxly coiled nuclei. 



These nuclear shells are thin, easily eroded, and it is frequently a 

 matter of no little difficulty to find a single intact nucleus, even in a 

 very large series of specimens of a single species. As the animal 

 grows it either forms septa behind it as the viscera are withdrawn 

 from the nuclear shell or fills the latter solidly up with shelly mat- 

 ter. This septum is often bulbous exactly as in nuclei of the type 

 above mentioned (No. 1) and may later be solidly filled up internally 

 with a shelly deposit. If the species had originallj'^ a nucleus of the 

 type about to be described, and this thin shell be eroded away as is 

 common, the septum-tip may remain, and so closely resemble the bul- 

 bous type as to deceive the very elect. One must therefore be on the 

 alert for a wholly intact nucleus, and if possible secure it from a 

 very young specimen. The best come from ovicapsules where the 

 young shells are ready to emerge but have not yet been exposed to 

 the erosive properties of seawater. 



The third type above referred to^ so nearly resembles the apex 

 in the genus Caricella of the Volutidae, that one suspects the pres- 



1 For Illustrations of the different types of nucleus which parallel one another in the 

 Chrysodomiae and Volutidae see Friele in Norwegian North Atlantic expedition, Mol- 

 lusca, pt. 1, pis. 1-3 ; and Dall, Trans. Wagner Inst., vol. 3, pt. 1, pis. 6 and 7, as 

 follows : No. 1, Friele, pi. 1, fig. 12 a-b ; No. 2, Dall, pi. G, fig. 3a ; No. 3, Dall, pi. 6, fig. 

 6; No. 5a; and Friele, pi. 1, fig. 11& ; No. 4, Dall, pi. 6, fig. 6, and Friele, pi. 1, fig. 106; 

 No. 5, Dall, pi. 6, fig. 8. 



