329

CARBONIFEROUS CEPHALOPODS.
BY ALPHEUS HYATT.

The following descriptions, accompanied by figures in outline, were taken from a collection forwarded by Mr. E. T. Dumble, State Geologist of Texas, and other fossils which were in my possession as loans from the National Museum and various persons referred to in the text. These forms being extremely limited in their chronological distribution, and therefore very helpful in distinguishing the age of the rocks in which they are found, it was thought best to have them all published in one treatise. This proceeding also enabled the author to make more satisfactory comparisons, and as these comprise a larger number of species than has yet been got together in a single publication it will be more satisfactory to working geologists.

NAUTILOIDEA.

TEMNOCHEILUS CONCHIFEROUS, n. s.

Loc. Texas.
Coll. Geol. Survey of Texas.
Figs. 23, 24, natural size.

This is a small species having an exceedingly thick shell. The sides are decidedly convex and ornamented with short, thick, heavy-looking, fold-like pilæ, which are prolongations of the thick, heavy, but not very prominent nodes on the edges of the abdomen. The shell is so thick that in some casts of the interior, as in the figure given above, these nodes are not visible, and in others they are only slightly indicated. The surface appears to have been smooth with the exception of these nodes and pile, but this could not be observed satisfactorily. The increase by growth in the transverse diameters is exceedingly rapid, whereas the vertical diameters increase slowly by growth. The abdomen is much depressed, almost flattened along the centre, becoming strongly convex only near the outer edges or sides. The sides, as in all the species of this genus, converge very rapidly towards the umbilici.