104 ROYAL SOCIETY OF CANADA 



pod analogous to the Tertiary Theeosomata," and he 8a3'8, " 1 cannot 

 admit amonp^ the Theeosomata the so called Primary Pteropods." At 

 page 1>."Î. lie f-ays. "ITyolitlies is distinguished from all Pteropods b}' their 

 triangular form, their partitions and their opereulum, which in no respect 

 resembles that of any operculate mollusc. 



Since Pelsinoer has rejected the Ilyolithidte from among the Ptero- 

 ]>0(la. and declares that they cannot tind a resting place in thai group, it 

 becomes necessaiy to seek for their living analogues. 



For a number of years I have been convinced that these shells some- 

 times heavy and thick, and frequently associated with littoral species, could 

 not have any relation to Pteropods. but was not prepared to suggest another 

 relationship, and so left them among the Gasteropoda. Late observations 

 among the primitive forms of the Etcheminian system described in the 

 succeeding article have led me to the conclusion that the proper place for 

 the llyolithidic is among the Marine Worms. This inference is made 

 chiefly on the basis of the observed larval stage, the later stages of growth, 

 and the nature of the operculum. 



One objection to considering the Hyolithidœ Gasteropods is that we 

 can detect nothing answering to the Protoconch of the Molluscs ; but 

 on the contrary the initial part of the shell, Avhen preserved proves to be 

 a slender, terete tube, varying from cylindrical to narrowly conical, and 

 in a number of species found to be divided into short segments by delicate 

 diaphragms.' 



This condition is parallel to what we tind in many sea-worms, as for 

 instance in Phyllochœtopteris claperadi ^ in which the tube, in form and 

 consistency; may be compared with the larval part of the tube of Hyo- 

 lithellus (?) flexuosus} The rigid and quill-like tube of Hyalinœcia tubicola* 

 also may well be compared with those of species of Urotheca de- 

 scribed in this article, which has a long, slender tube like that species ; 

 and which, like that of the species in question, is chitinous. Some annu- 

 lated tubes as Plagostegus ornatus, Sow., are seen to taper to a slender point 

 like JlyoUthes caudatus ^ of the Paradoxides beds at St. John, others are 

 stout and truncated {Nathria pycnobranchiata^) like many species of 

 Hyolithes. 



It is to Serpula, however, and Ditrypa that we may look for closer 

 parallels to Hyolithes, which has a calcareous tube. Ditrypa both in size 

 and form, approaches specie.-* of Orthotheca, and although the latter, in 



' For an earlier account of these structures in the Hyolithida' see Can. Rcc. Sci., 

 vol. 1, no. 3, p. 149, flfCH. 1 to 3. (N.B.— The numbers have been misplaced for tigures 

 2 and 3.) 



- Challenger Rep., vol. xii., p. :{74, pi. 4."), ligs. 10 and 12. 



3 Descril)ed in this article. 



< Challenger Rep., vol. xii., p. \m\ pi. 40, fig. 1. 



» Trans. Roy. Soc. Can., vol. iii., pt. iv., p. 53, pi. vi., figs. 5, 5a. 



« Challenger Rep., vol. xii., p. 319, pi. 40, flg. 13. 



