NO. 12 SPENCE SHALE AND ITS FAUNA— RESSER 23 



SPENCIA, n. gen. 



Small trilobites characterized by a rather large, slightly tapered 

 glabella which extends to the anterior furrow. Brim reduced to 

 thickened rim, wider in the middle than at the ends. This causes the 

 anterior furrow to join the dorsal furrow in front of the glabella. 

 Fixigenes convex, anteriorly nearly as wide as the glabella. Eyelines 

 fairly prominent. Eyes small, situated slightly behind the middle of 

 the head. 



Libragenes small, with short but sharp-pointed genal spines. 



Thorax has i6 segments. The pygidium is small, trilobate, and 

 well fused. 



Surface of cranidium and ridges of the thoracic segments marked 

 by scattered granules. 



Genotype. — S. fypicalis, new species. 



SPENCIA TYPICALIS, n. sp. 



Plate 6, figs. 22-25 



This species is characterized by scattered granules and a rather 

 wide space where the anterior and dorsal furrows join. 

 Locality 55c. 

 Holotypc and paratypes. — U.S.N.M. no. 96535. 



SPENCIA PLENA, n. sp. 



Plate 6, figs. 19-21 



This species is characterized chiefly by the swollen rim and the 

 narrowing of the preglabellar area or rather the anterior and dorsal 

 furrows. Scattered granules occur on the more elevated portions of 

 the cranidium. 



Locality 55c. 



Holotypc and paratypes.- — U.S.N.M. no. 96536. 



STAUROHOLCUS, n. gen. 



Small trilobites; only cranidia known. Glabella al)OUt three-fourths 

 the length of cephalon, without furrows, truncate with rounded 

 anterior corners, tapering only slightly. Fixigenes fully as wide as 

 glabella. Eyelines faint, but clearly defined. Eyes small, situated 

 about the mid-point. Occipital spine present. Brim rounded at an- 

 terior corners. Rim thickened in center, upturned. Preglabellar area 



