182 Transactions. — Zoology. 



very narrow, almost covered ; aperture rather oblique, rotundly lunate ; 

 peristome acute, straight, the margins not approaching ; columellar margin 

 obliquely ascending, slightly reflected and thickened. Diameter '5 inch. 



Hab. Napier. 



The generic position of this shell is very doubtful, it somewhat resembles 

 H, ignifiua, but differs in its very narrow umbilicus. The only specimens I 

 have seen were old and rubbed. 



Therasia t amor a, n. s. 



Shell small, conical, umbilicated, with membranous plaits : colour horny 

 brown. Spire conical, rather acute ; periphery sub-angled ; suture im- 

 pressed : whorls 5-6, rather flattened, finely striated and with irregular 

 distant membranous ribs, easily rubbed off : umbilicus narrow, but open : 

 aperture transversely oval ; peristome thin, the margins converging. 



Greatest diameter -16, least -14 ; height '10 inch. 



Hab. Auckland (T. F. Oheeseman). 



Differs from celinda in the open umbilicus, and from decidua in being 

 more conical and smaller. I place it with celinda, decidua, and Ophelia into 

 a separate genus called Therasia, having the dentition of Charopa with the 

 shell of Thalassia. 



Therasia thaisa, n. s. PL ix., fig. m., and pi. xi., fig. t. 



Shell rather solid, depressed, umbilicated, striated ; colour pale brown, 

 usually irregularly banded and marked with reddish brown. Spire conoidal, 

 obtuse ; whorls 5-5^, slowly increasing, rather flattened, more or less 

 obscurely angled, strongly but irregularly striated : suture impressed : um- 

 bilicus rather narrow, about one-seventh of the least diameter of the shell : 

 aperture rather oblique, rotundly lunate ; peristome thin, the columellar 

 margin rapidly ascending and rather reflexed. Greatest diameter •■£, least 

 '35 ; height -28 inch. 



Animal elongated ; the foot long and narrow, reaching beyond the shell, 

 rounded behind, slightly truncated and with a mucous gland situated under 

 a caudal papilla. Mantle sub-central, included ; body roughish : peduncles 

 long, cylindrical, approximated at their bases ; tentacles moderate. Top of 

 the head yellowish white, peduncles, tentacles, and a line down each side of 

 the head dark grey ; a broad longitudinal band of white, with a dark grey 

 line in the centre, runs along each side, and below this band the foot is 

 edged with alternate broad grey and narrow white transverse bands. 



Jaw arcuate, with flattened ribs which indent the concave margin. 



Dentition, 27-1-27 ; varying from 26 to 28. Laterals about 16. 



Central tooth rectangular, longer than broad; the reflexed portion short, 

 sharply constricted near the base and with a small cutting point. Laterals 

 with the base oblique, the reflexed portion bicuspid, the inner cusp single, 



