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, C). Shell long, ventricose, depressed ; apex sharp- 
pointed, constricted in front ; aperture slightly canaliculated and compressed laterally. 
Cross-section elliptical. Upper Cretaceous to Recent. 
Cuvierta, Rang; Triptera, 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. Ordovician to Devonian. 
Tentaculites, Schloth. (Fig. 1023). This, the 
solitary genus, is prodigiously abundant in the 
Silurian and Devonian, 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 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. 



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Fic. 1023. 
A, Tentaculites  scalaris, 
Schloth. Erratic block of 
Ordovician age; Berlin. B, 7. 
ornatus, Sowb. Silurian; 
Dudley, England. OC, T. 
acuarites, Richt. Silurian 
concretion ; Thuringia. <A 
smaller individual contained 
within the larger (after 
Novak). 
Family 2. Torellellidae. Holm. 
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 
f ; > Py ; ( ; 
triangular, elliptical, or lenticular ; one side often flattened, and the other arched or with 
