572 



MOLLUSCA 



PHYLUM VI 



Tentaculites Scliloth. (Fig. 1073). Tliis, the solitary genus, is prodigiously 

 abundant in the Sihirian and Devonian, the strata being sometimes fairly charged 

 with their remains. Tlie sliell is composed of a comjjact outer layer, and an inner 

 layer made up of thin lamellae running parallel witli the external surface. 

 The supposed Tentaculites described from the Oligocene by Ludwig and Blankenhorn 

 are thin-shelled, transversely ribbed, conical tubes, wliich probably belong in the 

 neighbourliood of Stijliola or Euchilotheca. 



Family 2. Torellellidae Holm. 



Thick - loalled, smooth, transversely or longitudinally striated, straight or bent tubes, 

 acutely terminated "posteriorly, and. unthout opercula. Cambrian to Silurian. 



Turellella Holm. Tubes strongly compressed, flattened at both ends, elliptical in 

 cross-section, and with fine transverse striae ; composed of brownish-coloured calcium 

 phosphate. Cambrian to Silurian ; Sweden. 



Hyolithdlus and Salterella Billings ; Coleolus Hall ; and Goleoloides Walcott, from 

 the Lower Cambrian of North America, j^robably also belong here. 



Family 3. Conulariidae Walcott. 



Shell rectilinear, elongate- conical, rectangular to rhombic in cross- section, with 

 usually sharp edges, acute or truncated posteriorly. Each of the transversely striated or 

 ribbed lateral faces divided into longitudinal halves by a superficial groove, corresponding 

 internally to a median ridge. Posterior portion of the shell divided off by septa. 



A])erture constricted by four triangular or linguiform incurved 

 lobes of the anterior margin. Ordovician to Jura. 



Conularia Mill. (Figs. 1074, 1075). This, the solitary 

 genus, sometimes attains a length of 20 cm., and is represented 

 by about 100 species. Its maximum distribution occurs in the 

 Ordovician and Silurian of Bohemia, Normandy, England, 

 Sweden and North America, and in the Devonian of North 

 America and Bolivia. It is rare in the Carboniferous and 

 Permian,- and the last surviving species occurs 

 in the Tiias and Lias. 



Order 2. PULMONATA Cuvier. 



Air-breathing Snails.^ 



Euthyneura in wldch the gill cavity is 

 transformed into a lung for breathing free 

 air. Mainly terrestrial or fresh-water forms. 



A few Pulmonates have reverted to ex- 

 clusively aquatic habits, and have the lung 

 . , , 'i'^"'}' filled witli water ; and in a few, secondary 



risulcata Sowb. ' -mi 



Upper Carboniferous gills are developed in the cavity. These, 

 Sc;raaM'!''fhS' however, are rare exceptions. The great 



Fig. 1075. 



Conularia 



Fig. 1074. 



Conularia aw^mnhi Barr. 

 Ordovician (Etage D) ; 

 Drabov, Bohemia. 



well-preserved aper- maioritv of forms breathe air by means of a 



tural margins (after / i p i n i ^ j ii 



Etheridge). network 01 blood - vessels spread upon tlie 



inner surface of the lung. The ordinary 

 aquatic forms come to the surface of the water at intervals to renew their su2:)ply of 



^ Sandbergcr, F., Land- unci Siisswasser-Conchylien der Vorwelt. 1870-75. — White C. A., 

 Review of Aiiiericiui non-marine MoUusca. 3rd Ann. Rep. U.S. Geol. Siirv., 1881-82. — Tryun, 

 G. W. an<l ]'i/sbri/, II. A., Manual of Conchology, Pnlmonata. 



