CLASS IV 



GASTROPODA 



571 



In the Devonian of Bohemia, Nassau, Ural and North America, great niimbers of smooth, 

 circular, longitudinally striated tubes are occasionally met witli, the posterior end of whichis 

 intlated into a sniall bulb. Similar tubos have also been described by Blankenhorn froni the 

 Cretaceous of Syria. None of these differ externally to any great extent froni Clio or Styliola. 



Vaginella Daudiii (Fig 

 slightly canaliculated and 

 Cretaceous to Recent. 



Guvierina Boas ; Triptera 

 O. Meyer). Tertiary and Re(;ent 

 Fisclier. Eocene. 



1070, C). Shell long, 

 compressed laterally 



ventricose, depressed ; aj)erture 

 Cross-section elliptical. Upper 

 AB c 



Qiioy {Tihiella 

 Euchilotheca 



Fig. 1072. 

 , A, B, Hyolithes elegans Barr. 



Family 3. Hyolithidae Nicholson. 



Shell symmetrical, conical or pyramidal, 

 straight or sharply hent ; cross-section triangulär, 

 elliptical or lenticular ; one side often ßattened, 

 and the other arched or with a Munt median keel. 

 Surface smooth or ivith fine transverse Striae, rarely 

 longitudinally striated or ribhed. Aperture com- 

 pletely closed by an operculum, the latter being 

 semicircular, triangulär or lentiform, with lateral 

 nucleus, and concentrically striated ; fteropodia, 



with a chitinous support to the anterior edge. f^^g ^^'' 1^°^«'"««' B«^«"^^* 

 Cambrian to Permian. 



According to Holm the typical genus, 

 Hyolithes Eichwald {Tlieca Sowb. ; Pugiunculus 

 Barr.) (Fig. 1072), is divisible into two subgenera. One of these, Orthotheca Noväk, 

 contains forms with an abruptly truncated anterior end ; and in the other, Hyolithes 

 s. Str., the margin of the flattened side projects somewhat above the opposite wall. 

 ABC The forms known as Gleidotheca, Gentrotheca Salter, 

 Gamerotheca, Diplotheca Matthew, Pharetrella Hall, 

 Geratotheca and Bactrotheca Noväk, fall within the 

 synonymy of Hyolithes. TJiis genus is abundantly 

 distributed in the Cambrian, Ordovician and Silurian 

 of North America, Great Britain, Sweden, Russia and 

 Bohemia ; it occurs sparingly also in the Devonian, 

 Carboniferous and Permian. 



Pterotheca Salter ; Phragmotheca Barrande. Silu- 

 rian ; Europe. Matthewia Walcott. Cambrian. 



Ordovician ; 

 Slightly re- 

 C, H. tnctximas Barr. Caiiibrian 

 (Etage C) ; Mleschitz, Bohemia. Anterior 

 portion restored, with operculum, and viewed 

 from the side. 1/2. D, Operculum (after Bar- 

 rande). 



Fig. 1073. 



A, TentacuUtes scalarif 

 Schloth. Erratic block of 

 Ordovician age ; Berlin. B, 

 T. orwitiis Sowb. Silurian ; 

 Dudley, England. C, T. 

 rtrudritfs Rieht. Silurian con- 

 cretion ; Thuringia. A 

 smaller individual contained 

 within the larger (after 

 Xovak). « 



Suborder D. CONULARIIDA Miller and Gurley. 



Paleozoic forms of doubtful systematic position, 

 resembling some Recent Pteropoda, but probably to be 

 regarded as a parallel rath^r than as an identical 

 group. 



Family 1. Tentaculitidae Walcott. 



Thick - walled, , tapering, elongate, conical tubes, 

 having a circular cross-section, and terminating posteriorly either acutely or in an 

 embryonal bulb. Surface ornamented with parallel raised transverse rings. TJie apicaJ 

 portion of the shell often filled with calcareous matter, or divided off by transversr a< fiia. 

 Ordovician to Devonian. 



