PTEEOPODA. 



51 



Fig. 443 

 nata 



M. Barrancle enumerates eigiity-three species of Connlaria, 

 most of which are Palaeozoic, commencing in the lowest 

 Silurian deposits. The genus, however, 

 extends into the Mesozoic rocks, the last 

 species, so far as at present known, ap- 

 pearing in the Lias. 



Lastly, the genus Tentaculites com- 

 prises a number of singular Palaeozoic 

 fossils, the true position of which cannot 

 be said to be absolutely free from doubt. 

 Most authorities now place Tentaculites, 

 with apparently good reason, in the Ptero- 

 poda ; but others would still refer this 

 genus to the Tubicolar Annelides. It 

 must be admitted, also, that in some 

 respects Tentaculites approximates pretty 

 closely to the Annelidous genera Conchicolites and Cornulitcs.^ 

 Upon the whole, however, the mode of occurrence of Tenta- 

 culites, and its undoubted free habit of existence, leave little 

 doubt as to its true place being amongst the Pteropods. The 

 shell of Tentaculites (fig. 444) has the form 

 of a straight conical tube, tapering towards 

 one extremity to a pointed closed apex, and 

 expanding towards the other to a circular 

 aperture. The walls of the shell are thin, 

 and are surrounded with numerous thickened 

 rings or annulations, sometimes with inter- 

 mediate stria3, over a whole or part of the 

 length of the tube. The size of Tentaculites 

 varies mucli in different cases, being some- 

 times less than a couple of lines in length, 

 and sometimes attaining a length of an inch 

 or more. Pifty-two species of Tentaculites 

 are enumerated by M. Barrande, commencing in tlie Lower 

 Silurian and ranging into the Devonian. The genus is, 

 however, principally Silurian, and examples of some species 

 often occur in myriads through a considerable thickness of 

 strata. 



The typical species of Tentctculites possess an annulated 



Fig. 444. — Tentacu- 

 lites ornatus. Upijer 

 Silurian. Europe ancl 

 Nortli America. 



