314 (WKBONIKKKDUS FORMATIONS AND FAUNAS OF COLORADO. 



W'liilc these shells iirc similar to the Geneviovc species, AV. ffpergenensin, they 

 sliow fully as close resemblance to St. amiium of th(\ Kiiiderhook and lower Burling- 

 ton periods, or tlioy might he regard(Ml as a slightly undersized variety of 8t. 

 DuieritmphaluK Win., also of the KinderhooU; and it is ([uitc possible that they are 

 oidy immature spccimiMis of some such species as St. lu.mix, the younger stages of 

 wl\it'h they closely imitate. 



Localiti/ (tiiil horizon. — Leadville district (stations 2374, 2376); Leadville 

 limestone. 



LOXONEMA Phillips, 1841. 



LOXONEMA? sp. 



This rather striking form has been obser\'ed at three localities. Two of these 

 (stations 2350 and 2358) ai'e in the Crested Butte region; the other (station 2363) in 

 the Aspen region. Though the material obtained is so jDoor as to render even its 

 generic reference uncertain, there is considerable probability that in each occurrence 

 the species is the same. It is a large, elongate, spiral shell, with a diameter below 

 of perhaps 35 ram. or more and an altitude of certainly not less than 60 mm. 

 There must have been seven or eight whorls. The surface appears to have been 

 smooth. A similar and perhaps identical form occurs in the Chouteau limestone of 

 Pettis County, Mo. 



Locality and horizon. — Crested Butte disti'ict (stations 2850, 2358); Leadville 

 limestone. Aspen district (station 2363); Leadville limestone. 



PLEUEOTOMARIA Def ranee, 1824. 

 Pleukotomaria ? sp. a. 



Shell small; greatest diameter, 10 mm. Spire low, probably not exceeding 

 7 mm. from the middle of the inferior portion to the apex. Whorls, probabh' 

 three or four. Umbilicus, probably closed. Peritreme, flattened above (for about 

 2.5 mm. near the aperture) and gently sloping downward. There is a strong 

 angulation where the return contour begins, the remainder of the outline being- 

 formed by a rather full curve. A short distance below the angulation, where the 

 surface is still nearly vertical, two ridges, jarobably representing a comparatively 

 broad band, are seen. The upper, which is the stronger, is about 1.5 mm. below 

 the angulation. 



A single specimen, an internal cast, is all that has yet been discovered of this 

 species. No sei-ious effort has been made to determine its specific affinities, and 

 it is probably indeterminable. It is certainly distinct from the Pleurotomaria 

 represented by an impression from Larimer County. 



Locality and harizon. — Canyon (station 2366); Millsap limestone. 



