STATE GEOLOGIST. 81 



SUB-FAMILY II.— LYNCEINiE. 



Intestine coiled; anus near the end of the post-abdomen; open- 

 ing of vas deferens nearly terminal. There are no anterior ceeca 

 but usually a single anal diverticle of the intestine. Rarely or never 

 more than two embryos produced at once. 



Series A. 



Head or dorsal line keeled or ridged ; abdomen long ; shell marked witli ^(agonal 

 striffi. This section is proposed for the old genera Camptocereus, Acroperus and Alo- 

 Hopsis, which seem to form a natural group though passing directly into Al ma. 



II. — Genus Camptocercus {> Camptocereus, Baird). 



This easily recognizable genus contains two groups, each with 

 several nominal species, which are distinguished mainly by the 

 width of the post-abdomen. In both the shell is elongated, more 

 or less quadrangular, longitudinally striate, armed behind with one 

 to four minute teeth. The head and back are keeled and the former 

 strongly arched. The antennules rarely extend beyond the beak 

 and are commonly curved laterally. The eye is proportionately 

 small. The post-abdomen is long and furnished with a lateral row 

 of scales. The terminal claws have a single basal spine and are 

 serrate. There is an ephippium, and the male opening is in front 

 of the terminal claws. 



Sub-genus 1. — Acroperus, Baird. 



Post-abdomen broad, margins parallel; anal teeth very minute 

 lateral scales large and usurping their place. Antennge with eight 

 setae (§n). Three species are described, one of which is very abund- 

 ant in Minnesota. 



Sp. 1 . Acroperus leiicocepliahis, Koch. 

 (Plate E, Fig. 5. Plate I, Fig. 9.) 



Lynceus leucocephalus, KOCH, FISCHER. 



Acroperus harpw, BAIKD. 



Acroperus leucocephalus, SCHOEDLER, P. E. MUELLER, KURZ. 



Acroperus sp., HERRICK. 



Acroperus striatus.JVRiyE, M.EDWARDS, LiEviN, lilljkborg, leydig, etc., se' 



to belong here, but I am able to add nothing to the eluci- 

 dation of the puzzle. 



Body rounded above, angled behind; head moderately arched and 

 carinated. Lower margin of the shell pectinate, terminating in 

 6 



