1902.] AND ANCIENT GEOGRAPHY. 279 



Mississippi valley to the neighborhood of the Great Lakes. To this 

 latter extension of the range also belongs C. pellucidus. South- 

 ward, this group goes through Texas (here it has been found near 

 the Mexican boundary line), and is found in the neighborhood of 

 the city of Mexico (C wiegmanm). Whether this latter locality is 

 connected with the localities in Texas or not is unknown. 



The centre of distribution of the second group is to be found in 

 the Southwest. We know two species from Mexico, two from New 

 Mexico, Texas and Kansas. Another species (C gracilis) extends 

 from these parts northward (in the prairies), and is found in 

 Kansas, Iowa, Illinois, as far as Wisconsin. In the South we have, 

 more or less isolated, C. clypeatus in Mississippi, and absolutely 

 isolated are C. carolinus and advena in South Carolina and Georgia 

 and C. ctibensis in Cuba. 



Within this group we observe a very striking discontinuity ; not 

 only the Mexican localities are separated from those in the United 

 States, but also in the Gulf States, the southern Atlantic States and 

 in Cuba there are representatives of this group, separated from the 

 rest in the Southwestern and Central States. 



Very different is the range of the third group. Here we have 

 complete continuity, and the centre is evidently in the system of the 

 Allegheny mountains and in the East. The species are very 

 numerous in the mountainous parts of Tennessee, Kentucky, North 

 Carolina, Virginia and West Virginia, Maryland, Pennsylvania, and 

 in the adjoining parts of Ohio and Indiana. This group is also 

 well represented in Illinois, and extends, gradually decreasing in 

 density, westward into Wisconsin, Minnesota, Iowa, Missouri (in the 

 eastern part only), Arkansas and the Indian Territory. It is very 

 rare in Texas, Louisiana, Mississippi ; is slightly represented in 

 Alabama, Georgia and South Carolina, but is wanting in Florida. 

 In a northeasterly direction, a single species (C bartoni) extends 

 over New York and New England across the Canadian boundary 

 into New Brunswick, where it reaches the Restigouche river, a 

 tributary of the Gulf of St. Lawrence. The same species is found 

 in the northern affluents of Lake Ontario (Toronto) and the St. 

 Lawrence river in Quebec (St. John's Lake), where it marks the 

 northern boundary of the genus. In Michigan this group is repre- 

 sented in the neighborhood of Lake Huron, but it has not been 

 found north of the Great Lakes in Canada. The northeastern 

 extension of the range of this group, on the one hand, is very 



