142 University of Texas Bulletin 



on each side by a low, non-tuberculate ridge. The ridges are wider and 

 more prominent than in our species and the intervening spaces much nar- 

 rower ; the tubercles are more widely spaced ; the fine secondary revolving 

 lines are apparently lacking; and the contour is more angular. Roemer's 

 species is also figured as having a smaller apical angle (about 12 degrees). 



TURRITELLA WORTHENSIS n. sp. 

 PI. 10, fig. 42 



MEASUREMENTS: Type length of fragment 26 mm.; width (esti- 

 mated) 14.5 mm. 



HORIZON: Basal Weno formation, marl facies. Abundant in the 

 Fort Worth region in association with Ancycloceras bendirei, Remondia 

 acuminata and Pecten georgetownensis. 



LOCALITIES: 618, near Fort Worth, Texas (type locality); exten- 

 sively distributed in Tarrant County, Texas. 



DESCRIPTION: Shell conical, steeply turreted, apical angle 23 de- 

 grees, with six or more volutions. Shell nearly straight sided, sutures 

 impressed, surface with usually six nearly elevated spiral ridges bearing 

 conspicuous, equal, equally-spaced, rounded tubercles. Beneath this are 

 two parallel thin spiral ridges with obsolete tubercles. These form the 

 bottom of the volution, and the uppermost of the six ridges mentioned, 

 which is longer than the others, forms the top. Between each two ridges 

 are four to six fine non-tuberculate spiral lines, but exceptionally one or 

 two of these may be thickened, giving the appearance of an alternating 

 series of fine and coarse revolving ridges on the volution. In most of the 

 material at hand the six revolving ridges are equally spaced, and are sep- 

 arated by a depression only slightly wider than one of the ridges. The 

 tubercles are equally spaced on all the ridges, and number about 65 on 

 the last volution. These tubercles decrease in size on the earlier volutions, 

 and all are present in the youngest stage examined. 



Transverse growth lines are not visible. The details of the aperture 

 are not preserved. The cross-section is rounded and triangular, the ex- 

 ternal side of the volution being longest. Below the shoulder of the usually 

 tuberculate volution are about four impressed lines, of which the two al- 

 ready mentioned are not covered by the succeeding volution. Below this 

 point the volution is smooth. 



Many species of Turritella have been described from the Texas Coman- 

 chean, and some of these are indeterminate, on account oi faulty figures 

 and description, or lack of necessary information concerning stratigraphy 

 and locality. 



