572 



MOLLUSCA 



PHYLÜM VI 



Tentaculites Schloth. (Fig. 1073). This, the solitary genus, is prodigiously 

 abuiidaiit in the Siluriaii and Devon ian, the strata being sometimes fairly charged 

 with their remains. The shell is composed of a compact outer layer, and an inner 

 layer made up of thin lainellae running parallel with 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 

 neighbourhood of Styliola or Euchilotheca. 



Family 2. Torellellidae Holm. 



Thich - ivalled, smooth, transversely or longitudinally striated, straight or bent tuhes, 

 acutely terminated posteriorly, and without opercula. Cambrian to Silurian. 



Torellella 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. 



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

 the Lower Cambrian of North America, probably also belong here. 



Family 3. Conulariidae Walcott. 



Shell rectüinear, elongate- conical, rectangular to rhomhic in cross-section, with 

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

 ribhed 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. 

 Aperture constricted by four triangulär or linguiform incurved 

 lobes of the anterior margin. Ordovician to Jura. 



Öonularia 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 Trias and Lias. 



Order 2. PULMONATA Cuvier. 

 Air-breathing Snails.^ 



Euthyneura in which 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 



filled with water ; and in a few, secondary 



iTpper Carboniferous gills are developed in the cavity. These, 



Limestone; Glasgow, i,^,,,^,,^^ „_ J_ .^„_^;.„. rvi. .„^ 



Fig. 1075. 



Conularia quad- 



risulcata 



5owb. 



Fio. 1074. 



Conularia anginala Barr, 

 Ordovician (Etage D) 

 Drabov, Bohemia. 



Scotiand. showing however, are rare exceptions. The great 

 weii-preseryed aper- majority of forms breathe air by means of a 



tural margms (after . i n n i ■, '^■, ^i 



Etheridge). network Ol blooQ - vessels» spread upon the 



inner surface of the lung. The ordinary 

 aquatic forms come to the surface of the water at intervals to renew their supply of 



^ Sandherger, F., Land- und Siisswasser-Conchylien der Vorwelt. 1870-75. — TFMe CA., 

 Review öf American non-marine Mollusca. 3rd Ann. Rep. U.S. Geol. Surv., 1881-82.— Tryow, 

 O. W. and Pilshry, H. A., Manual of Conchology, Puhmnata. 



