THE ANATOMY OF MEGALATRACTUS. 



By H. Lrighton Kestkven. 



I. — Introduction. 



II. — Anatomy of Megalatractus arctanus. 

 III. — Anatomy op Megalatractus maximus. 

 IV. — Anatomy of the Genus. 



V. — Comparative. 

 VI. — The Systematic Allocation of the Genus. 



I.— INTRODUCTION. 



The material used in the present investigation was derived 

 from three sources: — (1) examples of Siphonalia maxima, 

 Tryon, obtained during the Trawling Expedition of H.M.C.S. 

 " Thetis " in 1898 ; (2) specimens taken by the " Deep Sea and 

 Trawling Syndicate" ofiF Broken Bay in 1891 ; and (3) a large 

 example of Megalatractus aruaoius, Linn., obtained by Mr. C. 

 Hedley at Mapoon, at the mouth of the Batavia River, Gulf of 

 Carpentaria, Queensland, in May, 1903. Although the apex of 

 the shell and part of the body-whorl of the latter were broken off, 

 the state of preservation of the soft parts was not all that might 

 be wished. The visceral coil was in a thoroughly satisfactory 

 condition, but the preservative used, a mixture of formalin and 

 alcohol, was not strong enough to permeate the muscular tissue 

 of the body, and as a result the organs at the anterior end of the 

 body cavity were far from well preserved. The ganglia of the 

 nerve-ring, the salivary glands, the anterior portion of the oeso- 

 phageal loop and oesophageal gland, were found to be completely 

 destroyed. The nerves lay loose among these decomposed organs, 

 connective tissue and muscle strands, filling this part of the body 

 cavity. 



Nevertheless it is to this specimen that the present paper owes 

 a great deal of its completeness, for, whilst the organs of the body 

 cavities of most of the specimens of aS*. maxima were in a condition 

 fitting them for investigation, the visceral coils of these were 

 almost useless for the purpose, and Mr. C. Hedley* had suggested 

 a relationship between the two molluscs. 



* Hedley— Aust. Mus. Mem., iv., 1903, p. 375. 



