422 " THETIS " SCIENTIFIC RESULTS. 



spiral cords below the peripheral keel, and more distinctly spirally 

 Urate, the base nearly smooth. Aperture one-third the length of 

 the shell ; outer lip thin and fragile, columella lip distinctly 

 sigmoid, smooth. Alt. 21, diam. 6 mm," I am favoured with a 

 particularly fine series from the mass of nidamental capsules 

 described by Hedley,* and am able to add to this description. 

 The number of whorls may be stated to be five ; I exclude the 

 last of Pilsbry's description, but as the protoconch is ill-defined 

 from the succeeding neanic structure, the number of whorls may 

 vai'y with the development of the sculpture and in personal opinion. 

 The whorls may be so sharply angulated as to be aptly described 

 by the term " carinated," or they may be evenly rounded. The 

 character "obtusely nodulous" may vary from the verge of 

 extinction to a degree of development quite as great as that 

 indicated in Tryon's figure. f 



The obsolete spiral lirse are the first signs of the ultimate 

 adult sculpture, which may extend up the protoconch for three 

 or four whorls, or may only reach the penultimate ; but invariably 

 the actual line of extinction is not to be found. Pilsbry's descrip- 

 tion and the above remarks apply to the decollated protoconch ; 

 the portion lost is only a small thimble-shaped cup ; it vai'ies 

 both in the direction of its long axis and apparently in size — to 

 what extent may be gathered by a reference to fig. 120. 

 This apical portion, or veliger shell, is quite smooth, and 



is divided from the rest of 



the protoconch, or neanic (?) 



shell, by a deep groove or 



constriction. The apparent 



variation in size is due to 



the fact that the nucleus is 



shed in the same manner 



that a human tooth decays 



°' " ' and deposits fresh dentine, 



viz., as the outer layers are corroded off, new layers are 



deposited inside. 



The shell of six and one-half whorls described by Pilsbry is 

 possessed of the number of whorls that are present in most of my 

 specimens which were taken from the capsules, but it lacks four or 

 five millimetres of their length. The largest specimen contained 

 in the mass consists of nearly seven whorls, and measures 33 mm. in 

 length; the apical whorl has a diameter of 5 mm., the last whorl is 

 10"5 mm., whilst the penultimate is only 6 mm. in diameter. This 

 suddenly swollen whorl may be regarded as the first of the true 

 conch, though I believe that the whole pi'otoconch, except the 

 thimble-like apex, is neanic structure. 



* Hedley— Proc. Linn. Soc. N.S. Wales, xxv., 1900, p. 508. 

 t Tryon— Man. Conch., ix., 1887, pi xxvi., f. 16. 



