Solenoceras sp.

KENNEDY, W. J., LANDMAN, N. H., COBBAN, W. A. & SCOTT, G. R., 2000, Late Campanian (Cretaceous) Heteromorph Ammonites From The Western Interior Of The United States, Bulletin of the American Museum of Natural History 2000 (251), pp. 1-88 : 77-78

Solenoceras sp. Gill and Cobban, 1966: A54. Solenoceras mortoni (Meek and Hayden) . Scott

and Cobban, 1986b: map explanation.

TYPES: The holotype is USNM 482521 , from a sandstone concretion in the Terry Sandstone Member ( Exiteloceras jenneyi zone) of the Pierre Shale at USGS Mesozoic locality D304 near Fort Collins , Larimer County, Colorado (fig. 2, loc. 35). Paratypes are USNM 482522–482524 , from the same locality ; USNM 482525 and 482526 from the Terry Sandstone Member at USGS Mesozoic locality D303 (fig. 2, loc. 34) ; USNM 482527 , from the Pierre Shale at USGS Mesozoic locality D803 (fig. 2, loc. 44) ; USNM 482528 , from the Pierre Shale at USGS Mesozoic locality D986 (fig. 2, loc. 32) ; and USNM 482529 , from the Pierre Shale at USGS Mesozoic locality D8629 (fig. 2, loc. 48) .

ETYMOLOGY: From Larimer County, Colorado.

MATERIAL: Twenty specimens, all incomplete internal molds.

DIAGNOSIS: A very small species of Solenoceras with three or four ribs per limb height. Constrictions rare, but may occur on either limb (fig. 63).

DESCRIPTION: The holotype (fig. 61C) consists of two tightly appressed limbs connect- ed by a narrow elbow 4.4 mm in diameter. The total length of the specimen is 20.7 mm. The smaller limb is broken off at a limb height of 1.3 mm, where the whorl section is circular. Ornament of this limb consists of single, straight, prorsiradiate ribs; the rib index is 4; each rib bears a minute, nodate tubercle at the margin of the venter. Ribs greatly weaken on the elbow, but tubercles remain conspicuous there. About 13.3 mm of the larger limb is preserved; the adoral end has a height of 2.8 mm, although it is somewhat crushed laterally. Ribs are rectiradiate on the elbow and rursiradiate on the larger limb; they are single, narrow, and straight; the rib index is 4. The body chamber occupies the larger limb and elbow.

Seven paratypes ( USNM 482522 , 482523 , 482524 a–e), from USGS Mesozoic locality D304 (fig. 2, loc. 35), have elbow diameters of 4.7, 4.9, 5.2, 5.4, 5.5, 5.5, and 5.6 mm. Smaller limbs have whorls about as high as wide ; they have broadly rounded dorsums, well-rounded flanks, and slightly flattened, narrow venters. Larger limbs have whorls about as high as wide, and have prominent impressed dorsal furrows. Three paratypes ( USNM 482525 , 482526 a, b), from a nearby locality (D303), have elbow diameters of 4.7, 4.9, and 5.0 mm. Two paratypes ( USNM 482527 a, b), from another locality (D803), have elbow diameters of 4.8 and 5.0 mm. One of these specimens has two constrictions on the larger limb, each bounded by high adoral and adapical ribs .

The suture of Solenoceras larimerense , n. sp., is very simple. The external and lateral lobes and adjoining saddles are bifid, without further subdivisions (fig. 64).

DISCUSSION: The species differs from Solenoceras bearpawense in its much smaller size and slightly sparser ribbing. Solenoceras mortoni (Meek and Hayden, 1857) (p. 134) is slightly larger and has occasional constrictions; Solenoceras mexicanum Anderson, 1958 (p. 211, pl. 72, fig. 8), likewise, is a little longer.

OCCURRENCE: Solenoceras larimerense seems to be confined to the upper Campanian zone of Exiteloceras jenneyi . Most specimens are from the Terry Sandstone Member of the Pierre Shale in the Fort Collins area in northern Colorado. The species has also been found with Exiteloceras jenneyi jenneyi in the Pierre Shale near Red Bird, Niobrara County, Wyoming (fig. 2, loc. 22).