TIIIO AXATOMV OK MldlAI. ATliAC I'US — KICSTlvVK.V. 121 



already intimated, been concluded that both molluscs beloii;L,' to 

 the one genus, and are not worthy of even subgeneric distinction. 

 Under these circumstances two courses were open to the writer ; 

 one was to sink the term Meijalair actus and regard M. aruanus as 

 a Siphonalia, tiie other was to regard i6'. maxivia as a Mecjala- 

 traclns and retain both generic terms. This latter is the course 

 adopted, for the following reasons. If we sink the term Megala- 

 tractus, we, without sutiicient evidence, suppose that all the 

 species ranged under Sip/umalia have the same anatomical 

 characters as the two here discussed. Although all these species 

 probably do possess the same characters, it is better to leave the 

 matter open until additional, and more typical examples have been 

 investigated. 



I find that S'qihoiialia maxima has alread}^ been listed under 

 the generic name Jlei/alatractics by Miss M. Lodder in a list of 

 shells in the Tasmanian Museum.* 



The sense of my title, " The Anatomy of M eg alatr actus" and 

 my reason for treating M. aruaniis first, will now be apparent ; 

 the anatomy of the genus, or a summary of the two specific investi- 

 gations, is rendered in Part IV. of the paper. 



The absence of histological details is to be deplored, but the 

 state of preservation of my material put such investigations quite 

 out of the question. 



II.— ANATOMY OF 2IEGALATRACTUS ARUANUS, Linn. 



1. External features and pallial complex. 



a. — External Features. 



(PL xxxix., fig. 5, and PI. xl., fig. 2.) 



It is unnecessary to describe the shell ; this has already been 

 done several times, perhaps the best figure being that of 

 Reeve, t 



The protoconch (Fig. 119) " has a literature of its own," 

 as stated by Hedley in his "Studies on Australian 

 Mollusca, Part i."| This literature is there reviewed, 

 and the synonymy of the species discussed. My use of 

 the specific name aruanus is adopted from this paper. 



Pilsbry§ described the pi'otoconch thus: — "Cylindrical, 

 white, fragile, hardly tapering, consisting of 6h remain- 

 ing whorls, each carinated and obtusely nodulose in the ^"^*" ^'^^'^ 

 middle, and obsoletely spirally lirate. Last whorl with one or two 



* Lodder— Proc. Roy. Soc. Tas., 1900, p. 130. 



+ Eeeve — Conch. Icon., iv., Fusus, 1847, sp. 15. 



+ Hedley— Proc. Linn. Soc. N.S. Wales, xxv., 1900, p. 98. 



§ Pilsbry— 27)6 Nautilus, viii., 1894, p. 17. 



