330
The living chamber expands very rapidly and continuously outwards to the aperture in its transverse diameters, and varies from somewhat more than one-fourth to somewhat less than half of a volution in length. The aperture has a very shallow broad ventral, and lateral sinuses. The impressed zone on the dorsum is well marked, but the involution covers only the central part of the abdomen, leaving the whole area of the sides and the edges of the abdomen exposed.
The sutures have broad and very short ventral and lateral lobes, and cor. responding saddles at the angles of junction of the abdomen and sides; dorsal sutures were not observed. The siphuncle is of medium size and somewhat above the centre. The figure is approximately natural size.
TEMNOCHEILUS FORBESIANUS.
Nautilus Forbesianus. McChesney, Trans. Chicago
Acad., I, Pl. 3, Fig. 4a-b.
Loc. Texas.
Coll. Geol. Surv. of Texas.
The fossil No. 289a has exactly the form in section of the whorl, the large nodes, and sutures of this well known Carboniferous species. Its other affines are also Carboniferous. It resembles the Nautilus Acanthicus, Marie Tzwetaev, from the Upper Carboniferous in Russia, but from this it differs in the sutures, which are less sinuous on the sides, more closely arranged, and it is supposed that they do not have an annular lobe, which is a minute acute or V-shaped dorsal lobe in the centre of the larger dorsal lobe, although this fact was not ascertained. The sutures also resemble those of Nautilus Coxanus, Meek and Worthen, but the nodes are larger and less numerous, the ventral (outer side) is broader in proportion and also not so evenly and prominently convex. It differs from Temnocheilus latus, and Winslowi, Meek and Worthen, in having a whorl less depressed in proportion to its breadth—that is, the abdomino-dorsal diameter is longer in proportion to the broadest transverse diameter of the whorl in adults, and the nodes are less prominent. Otherwise'it approximates so closely to Temnocheilus latus of the Carboniferous of the Illinois Survey, and also of the Belgian Survey, that it might be readily mistaken for the young of that species.
TEMNOCHEILUS LATUS, Meek and Worthen.
Loc.
near Oswego, Kansas.
Coll. National Museum.
This is a much compressed and distorted fossil in shaly limestone, having a"
Cephalopods de la Section Superieure du Calcaire Carbonifere de la Russie Centrale, Mem. de la Comite Geologique, V, No. 3, 1888, Pl. 1, Fig. 1-2.
Geol. Survey of Illinois, V.