SUTER : NOTE ON TROPHON UMBILICATUS. 63 



specimens have shorter spines, which often become obsolete, the 

 shells becoming almost devoid of all ornamentation, being simply 

 spirally grooved and longitudinally costate ; this is Hutton's var. 

 espmosa qi M. odogomis. This great variability in size and sculpture, 

 and the presence or absence of an umbilicus, have, no doubt, been at 

 the bottom of all the confusion. I must not forget to mention that of 

 my three specimens from South Australia received as M. umhilkatui^, 

 T. Woods, one only has an umbilicus, the two others show no trace 

 of it ; otherwise they are alike. 



ON THE ANATOMY OF THE VITRINA IRRADIANS 

 OF PFEIFFER. 



By WALTER E. COLLINGE. 



(Plates V and vi.) 



The mollusc which forms the subject of the present communica- 

 tion, has at different periods, and by different writers, been relegated 

 to various genera. Originally described by Pfeiffer^ in 1S52 as a 

 member of the genus Vitriiia, it was placed by Theobald- in that 

 heterogeneous genus Helicarion ; as a member of this genus it was 

 treated of (or at least its shell) by Nevill"', Clessin^, Tryon"', and 

 others. In 1898 Lieut-Col. Godwin-Austen" intimated that he 

 proposed to describe a new subgenus for its reception, to which he 

 gave the name Ratnadvqna, and in the following year" he gave a 

 diagnosis and some brief notes on the anatomy of the generative 

 organs. The jaw and radula were shown to be of the type seen in 

 Hpmiplcda, and the male organ (only partially described) was 

 compared with that of Eapleda, Nihjiria, and Ariojjlianta, and 

 thouoht to be allied to the two latter. 



1 Proc. Zool. Soc. , 1852, p. 156. 



2 Supp. Catal., p. 24. 



3 Hand-list of Gastrop., 1878-85, p. 15. 



4 Nomencl. Helic, 1881, p. 31. 



5 Man. Conch., 1885 (ser. 2), p. 176, pi. 40, fig. 33. 



6 Proc. Malac. Soc. Lond., 1895, vol. iii, p. 253. 



7 Moll, of India, 1899, vol. ii, pt. ix, pp. 93-96, pi. l.\xxv, figs. i-8a. 



