l86 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 64 



ALOKISTOCARE POMONA, new species 



Plate 25, fig. 6 



General form elongate, with broad cephalon and thorax converg- 

 ing rather uniformly to the small, narrow pygidium. The cephalon 

 is characterized by its relatively narrow glabella and fixed cheeks 

 and broad free cheeks. One only of the species shows the median 

 boss of the frontal limb crossing the transverse frontal furrow. The 

 genal angles are produced into spines that extend backward some 

 distance beyond the ends of the thoracic segments. 



Thorax with 19 narrow segments; axial lobe strongly defined by 

 its convexity ; pleural lobes with the geniculation of the segments 

 at about two-thirds the length of the segment, where rather strong 

 straight pleural furrows bend backward and narrow to a sharp 

 point. 



Pygidium small, but details of structure unknown. 



Surface, as shown by casts in fine argillaceous shale, slightly 

 roughened by shallow pits. 



The only nearly entire dorsal shield has a length of 6 mm. for 

 cranidium, and 10 mm. for thorax. 



Observations. — This fine species dififers from other species referred 

 to Alokistocare by its narrow fixed cheeks ; broad free cheeks ; nar- 

 row postero-lateral limb, an.d elongate, narrow glabella with its 

 faint lateral furrows. With our present information it is placed 

 under this genus pending further discovery of closely allied forms. 



Formation and locality. — Middle Cambrian : ( isgf ) Wolsey shale ; 

 below Sixteen Station in Sixteen Mile Canyon, Meagher County, 

 Montana. 



Collected and presented to U. S. National Museum by M. Collen. 



ALOKISTOCARE ? PROSPECTENSE (Walcott) 



Plate 25, fig. 8 



Ptychoparia ? prospectensis Walcott, 1884, Monogr. U. S. Geol. Survey, 

 Vol. 8, p. 46, pi. 9, fig. 20. (Description and illustration of type speci- 

 men of cranidium.) 



Ptychoparia ? prospectensis Walcott, 1886, Bull. U. S. Geol. Survey, No. 30, 

 p. 202, pi. 27, fig. 5. (Reprint of previous description and a poor repro- 

 duction of illustration.) 



There is nothing to add to the original description of the type 

 cranidium except to note that I now think that the " finely granu- 

 lose " surface is produced by the minute ridges between shallow pits, 

 and that the surface is characterized by shallow pits rather than fine 



