252 GEOL. AND NAT. HIST. SURVEY OF MINNESOTA. 



Schoedler. I must here express my saspicion that the Pleuroxus 

 aculeatus, P. exlguus and P. excisus all belong under this species. I 

 have seen a small form which lacked the line striations; and there ap- 

 peared to me to be, at times, a slight indication of a second series of 

 hairs upon the post- abdomen. 



The form is oblong, truncate behind, variously arched above, but 

 usually with a rather low, evenly curved dorsal contour; the lower 

 shell margin is either nearly straight or convex in front and concave 

 along the posterior third, and is heavily beset with very long pectinate 

 bristles. The head is moderately depressed, with a very broad, blunt 

 and short beak (in some positions this beak seems acute, but it is an 

 optical delusion); the fornices are very broad, covering the antennules 

 completely; seen from above the head is broad and truncate in front; 

 the eye is larger than the large pigment fleck, which is nearer it than 

 the end of the beak. The antennse have eight setre, the last of which 

 is minute; the five spined ramus has a strong thorn on the end, and 

 the inner terminal seta is reduced. The post abdomen is rather broad 

 and truncate or somewhat rounded below; its length is very variable, 

 being short in small individuals; its form is subject to concomitant 

 variations. The seven to eleven anal spines extend in a series of minute 

 bristles above the anus. The lower posterior angle of the shell bears 

 one to four teeth; the marking consists of wavy ridges and strise, pro- 

 ducing, by the crossing of two sets springing from the two lower angles, 

 a reticulation covering mpre or less of the entire shell. The head-shield 

 and the spaces between these markings are densely striated. Color 

 yellowish, often opaque. Length 0.24 to 0.40 mm. At times abund- 

 ant. Birge alone has seen the males; his description agrees with Kurz's 

 account of the male of A. exigua, save that the former speaks of spines, 

 and the latter of thorns, along the post abdomen. 



Alonella exigiia Lilljeborg. 



Lynceus exiguus — Lilljeborg, Leydig, Fric. 

 Pleuroxus exiguus — Schoedler, P. E. Mueller. 

 ? Lynceus aculeatus — Fischer. 



Aside from the differences in the male sex as above indicated, this 

 form is said to have a convex lower margin, a rounded post-abdomen, 

 and the pigment fleck nearer the end of the beak than the eye. The 

 absence of the fine striation, finally, is the most marked characteristic- 

 Length 0.30 to 0.33 mm. Not identified in America. 



(?) Alonella grlsea Fischer. 



This species is included here on the authority of Kurz. The shell 

 may or may not be toothed at the lower corner, and is partly lined and 

 partly reticulate; but the only character which at all separates this 



