DESCRIPTION OF NEW SPECIES 419 



anterior four pairs diverge slightly, but the posterior half of each becomes 

 nearly parallel to the rest of the series. Ribs are somewhat elevated at 

 their proximal extremities on the dorsal furrow ; they end in free and 

 somewhat blunted tips. Ribs covered with tubercles, especially along 

 the edges. Length, 15 millimeters; greatest width the same; greatest 

 width of axis, 6 millimeters at its anterior. 



This species differs from other described species of Encrinurus in pos- 

 sessing a greater number of pygidial annulations and in the thoroughly 

 tuberculated character of the pygidium. 



Locality and formation, Bellefonte, Pennsylvania, in the lower Trenton 

 horizon. Collected by G. L. Collie. 



RIBEIRIA PARVA SP. NOV. 



Plate 59, figures 4 and 5, lateral and posterior views X 3 diameters 



Carapace small, ovate, compressed, 7 millimeters long, 5 millimeters 

 in height, 3 millimeters thick. Straight dorsal margin, with muscular 

 impressions faintly visible, bilaterally symmetrical ; antero-dorsal ex- 

 tremity notched ; the notch 1 millimeter long, extending toward the 

 center of the shell ; anterior rounded, posterior somewhat narrower than 

 the anterior, not so well rounded, somewhat appressed. The posterior 

 end slightly gaping ; surface apparently smooth. 



This species resembles R. nucidiiiformis Cleland, but differs in having 

 no fold or sinus. It is much smaller than R. calcifera Billings. 



Locality and formation, Bellefonte, Pennsylvania, in the middle 

 Beekmantown horizon. Collected by G. L. Collie. 



LIOSPIRA S TRIG ATA SP. NOV. 



Plate 59, figures 8 and 9, lateral and profile views 



Shell lenticular, spire depressed, conical, whorls four to five ; 4 centi- 

 meters in greatest diameter, convex above, passing into concave just 

 within the periphery. Edge slightly raised, forming a sharph^ defined 

 border; below concave beneath the border, then convex; umbilicus 

 nearly one-half the diameter, its edge subangular; slope of the whorls 

 within gently inclined toward the center ; height little more than one- 

 third the diameter. Surface of the upper side marked by broad, some- 

 what sigmoid elevations or ridges, with sharply defined depressions 

 between ; both ridges and depressions sweep backward somewhat strongly 

 on approaching the peripher}^ ; similar but fainter ridges below ; con- 

 centric lines parallel to the periphery visible on well preserved portions 

 of the shell. 



This form is very similar in general appearance to Pleurotomaria 

 canadensis Billings, but differs from that species in the surface orna- 

 mentation. The sigmoid ridges are much better defined in the Penn- 



