STATE GEOLOGIST. 105 



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 m 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 stri'cie, producing, by the crossing of two sets springing from 

 the two lower angles, a reticulation covering more of less of the 

 entire shell. The head-shield and the spaces between these mark- 

 ings are densely striated. Color yellowish, often opaque. Length 

 '0.24.-0.40 mm. At times abundant. 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. 



Sp. 4. Alonella exigaia, Lilljeborg. 



Z/ynce%is exiguus, lill.jkborg, leydig, fric. 

 A lonella exigua, sars, kurz. 

 Pleuroxiis cxigims, schoedlbe, p. e. mueller. 

 ? Lynceus aculeatus, fischeb. 



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 0.30-0.33 mm. Not identified in 

 -America. 



(?) Sp. 5. Alonella grisea, 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 species from the above seems to be the position and 

 form of the head, which is said to be blunt and nearly horizontal, 

 .as in Camptocercus rectirostris. Is this a transition to Grraptole- 

 'beris ? 



Sp. 6. Alonella pyg-mfea, Sars. * 



(Plate H. Fig. 7.) 

 Alona pygmcea, sars. 

 Pleuroxus transversus, schoedler. 

 A-lona transversa, p. e. mueller. 

 Jjyuceus nanus, ekic 

 -A lonella pygmcea, kurz. 



