490 



MOLLUSCA 



SUB-KINGDOM VI 



straight, elongated ; surface smooth or faintly striated ; dorsal groove not parallel to axis of the 

 shell, but slightly oblique, with only the anterior extremity (which ends in a rostrum) in the 

 median line ; embryonic portion ends in a pointed apex. Tertiary and Recent. 



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

 circular, longitudinally striated tubes are occasionally met with, the posterior end of which is 

 inflated into a small bulb. Similar tubes have also been described by Blankenhorn from the 

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



Vaginella, Daudin (Fig. 1021, (7). Shell long, ventricose, depressed; apex sharp- 

 pointed, constricted in front ; aperture slightly canaliculated and compressed laterally. 

 Cross-section elliptical. Upper Cretaceous to Eecent. 



Cuvieria, Rang; Triplera, Quoy (Fibiella, O. Meyer). Tertiary and Recent. 

 Euchilotheca, Fischer. Eocene. 



Sub-Order C. CONULARIDA. Miller and Gurley. 



Palaeozoic forms of doubtful systematic position, resembling some recent Pteropoda, 

 but probably to be regarded as a parallel rather 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 

 A B c parallel raised transverse rings. The apical portion of 



the shell often filled with calcareous matter, or divided 

 off by transverse septa. Ordoviciaii to Devonian. 



Tentaculites, Schloth. (Fig. 1023). This, tlie 

 solitary genus, is prodigiously abundant in the 

 Silurian and Devonian, tbe 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 lamellae running parallel with 

 the external surface. The supposed Tentaculites 

 described from the Oligocene by Ludwig and Blanken- 

 horn are thin -shelled, transversely ribbed, conical 

 tubes, which probably belong in the neighbourhood 

 of Styliola or Euchilotheca. 



FIG. 1023. 



A , Tentaculites sccdaris, 

 Schloth. Erratic block of 

 Ordovician age ; Berlin. B, T. 

 ornatus, Sowb. Silurian; 

 Dudley, England. C, T. 

 acuarites, Richt. Silurian 

 concretion ; Thuringia. A 

 smaller individual contained 

 within the larger (after 

 Novak). 



Torellellidae. Holm. 



Family 2. 



Thick-walled, smooth, transversely or longitudinally 

 striated, straight or bent tubes, acutely terminated pos- 

 teriorly, 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, Salterella, Billings, Coleolus, Hall, and Coleoloides, Walcott, from the 

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



Family 3. Hyolithidae. Nicholson. 



Shell symmetrical, conical, or pyramidal, straight or sharply bent ; cross-section 

 triangular, elliptical, or lenticular ; one side often flattened, and the other arched or with 



