234 CRUSTACEANS. 



Horizon and localities. — Lower Oarboniferous, Louisiana 

 (Lithographic) limestone: Hannibal, Louisiana, Chouteau 

 Springs ( Cooper county ). 



Proetus swallovi Shumaed. 



Proetus swallovi Shumard, 1855: Geol. Sur. Missouri, Ann. Rept., p. 196, pi. 



B, figs. 12a-b. 

 Proetus ( Phillipsia) swallovi Herrick, 1887 : Bui Denniscn Univ., vol. Il, p. 



58. 



Cephalic shield semicircular, arched ; exterior border rather 

 narrow, slightly elevated and marked by four or five filiform 

 lines ; marginal sinus narrow, shallow and rather poorly defined ; 

 posterior border of the cheeks rather wide and limited inter- 

 nally by a Shallow yet distinct farrow. Glabella tumid, con- 

 siderably elevated above the plane of the cheeks, and occupy- 

 ing about four-fifths the entire length of the head; it is rather 

 more than half as wide as long, regularly rounded in front, 

 with sides in front of the eyes convex; divided into four parts 

 or lobes by three rather shallow grooves on each side ; occipi- 

 tal segment convex, slightly wider than the base of the glabella, 

 and about as high; occipital furrow slightly curved toward the 

 front, narrow, rather deeply impressed, widest at the ends. 

 Facial suture slightly impressed. Cheeks elevated in the mid- 

 dle, sloping rapidly downward toward the borders. Eyes 

 reniform, moderately well developed, not quite as high as the 

 glabella ; visual surface minutely reticulated. Thoracic seg- 

 ments nine in number ; axial lobe much elevated, wider than 

 the lateral lobes, annulations wide, flattened in the direction of 

 the axis, and separated from one another by narrow but well- 

 defined grooves. Pygidium about as long as wide and equal 

 in length to the head, broadly rounded behind, moderately con- 

 vex, with a rather wide border ; median lobe as wide as the 

 lateral, moderately elevated, composed of seven flattened seg- 

 ments, which are separated by straight though very slightly 

 impressed sutures. Surface minutely punctate. ( Shumard.) 



Horizon and localities. — Lower Carboniferous, Louisiana 

 ( Lithographic ) limestone : Chouteau Springs { Cooper county ). 



