86 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 148 



nidium fairly sharp. Posterior area slender, considerably wider (tr.) 

 than occipital ring. 



Free check with relatively narrow and well-defined border ; border 

 furrow becoming obsolete along posterior portion of lateral margin. 

 Genal spine rather broad-based, flat on dorsal side, of average length. 



Pygidium slightly more than twice as wide as long ; axis prominent, 

 showing 2 rings plus a terminal, indistinctly segmented section, oc- 

 cupying more than two-thirds of pygidial length. Pleural regions with 

 2 pairs of broad pleural furrows and traces of interpleural grooves; 

 border flat, fairly wide. 



Surface of test smooth except for more or less distinct puncta in 

 the depressions, especially the anterior border furrow. Length of holo- 

 type cranidium 15 mm. 



Discussion. — The combination of cranidium and pygidium forms a 

 distinctive species. The cranidium differs from most of the known 

 species of Aphelaspis in the relative width of the palpebral area ; other 

 species that have a wide palpebral area {A. lata, A. buttsi) are quite 

 different in other cranidial features. The low glabella and tumid pre- 

 glabellar field recall A. laxa, in which, however, the palpebral area is 

 narrow and the palpebral lobes are more anteriorly situated. The 

 pygidium resembles none of the above-mentioned species, being simi- 

 lar to A. rotundata and A. palmeri. 



As far as can be ascertained from the scarce and mostly fragmentary 

 material, the species is rather variable in most of its features. At both 

 localities where it was collected, A. washburnensis occurs in associa- 

 tion with another species of Aphelaspis, possibly the same in both 

 cases. This second species seems somewhat intermediate between A. 

 walcotti and A. quadrata, but the material was deemed insufficient 

 to decide whether it should be identified with either of these two 

 species or described as a new one. Therefore this form appears as 

 Aphelaspis sp. undet. in the faunal lists. 



Occurrence. — The type locality is cnqV20, Washburn. In this sec- 

 tion the species occurs in association with Aphelaspidella macropyge 

 and Glaphyraspis declivis, above the strata holding A. walcotti and 

 below those with A. caniiro, A. laxa, and A. quadrata. In the Three 

 Springs section, a limestone lens holding Aphelaspis washburnensis 

 and possibly Aphelaspidella macropyge was collected at the same level 

 (cns/15) as beds yielding Aphelaspis camiro, A. laxa, and A. quad- 

 rata, but the latter 3 species were not associated with A. washburnensis 

 in the same lens. From this evidence it is clear that A. washburnensis 

 occurs near the base of the middle Aphelaspis zone. 



Types.— RoXoiy^t: U.S.N.M. 144655. Paratypes: U.S.N.M. 

 144656-7. 



