Page:Quarterly Journal of the Geological Society of London, vol. 29.djvu/111

(iv.) On the fibre between two elements at the ordinary distance from each, other, the centre of an apparently superfluous element unexpectedly appears. Of its four radii seen in the section, two of course are parts of the fibre on which the centre occurs; the other two normally have no radii with which they can combine, and as a consequence they bend away in opposite directions at about 45° from their fellows, and open into the octahedral fibres of adjacent hexradiate elements (fig. 5). Besides these, other variations occur (fig. 6).

Spicules. — Though siliceous spicules are well preserved in some flints and coprolites, yet a careful examination has failed to reveal their presence in silicified ventriculites (T. Smith) or in phosphatized ones. For all this the Ventriculites may have been spiculate sponges; in a section of a Brachiolites, and in one of V. tessellatus, I have found simple acerate spicules, with which were associated one or two hexaradiate ones; possibly, however, these may have been washed in from the sea-bed during; fossilization.

Identification of Species.

i. Ventriculites tessellatus (Toulmin Smith); Scyphia tessellata (Seeley); Spongia texturata (Quenstedt).

Quenstedt' s figure^[1] of this species is an excellent one; it is taken from a specimen from the Weisse Jura, and accurately reproduces the Cambridge form. Quenstedt refers Scyphia texturata and S. parallela (Goldfuss) to the same species^[2], as well as Alcyonites texturatus (Schlotheim^[3] and Parkinson^[4]). This latter identification appears to me very questionable, Parkinson's figure more nearly representing Ventriculites quincuncialis than V. tessellatus.

In the Royal College of Surgeons is a specimen from the Jurassic of Wurttemberg, labelled by Prof. Morris, Ventriculites texata (Munster), which is in every respect a fac-simile of our Cambridge species; and I believe S. tessellata (Seeley), S. texturata (Quenstedt), and V. texata (Munster) are identical with V. tessellatus (T. Smith).

The following is a description of our Greensand Ventriculites tessel-

1. Der Jura, Quenstedt, tab. 83. fig. 7, p. 683.
2. Petref. Germ., Goldfuss, tab. 2. fig. 9, tab. 3. fig. 3.
3. Petref., Schlotheim, p. 373.
4. Parkinson, 'Organic remains,' tab. 10. fig. 12.

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