280 ORTMANN — DISTRIBUTION OF DECAPODS [April 3, 



remarkable, while, on the other hand, we have a scarcity of it south 

 of the Allegheny system and west of the Mississippi. With the 

 exception of one isolated station of C. argillicola in Texas, this 

 group is not represented in the Southwest. 



The largest number of species is found in the fourth group. In 

 certain respects it corresponds, in its distribution, to the third, 

 namely, in its exceeding scarcity in the South and Southwest. It is 

 wanting in Florida, in the low parts of the Carolinas, of Georgia, 

 Alabama and Mississippi. It is also wanting in Louisiana, and in 

 Texas it is found only in the northeastern corner (near the bound- 

 aries of the Indian Territory and Arkansas). Beginning here, it 

 extends northward over the Mississippi-Missouri- Ohio basin, 

 becoming more abundant, the centre being situated, in this region, 

 in the States of Missouri, Tennessee, Kentucky, Indiana, Illinois, 

 Iowa and the southern parts of Michigan and Wisconsin. East- 

 ward this group enters Ohio, Pennsylvania, Virginia, Maryland, 

 New Jersey and New York, reaching its northeastern limit north of 

 Lake Ontario, near Toronto and Montreal. In Wisconsin it extends 

 to Lake Superior, and one species ( C. virilis) reaches from Minne- 

 sota, including the northeastern corner of North Dakota, to Lake 

 Winnipeg and the Saskatchewan river, the most northern locality 

 known for the genus. Westward, the range of this group includes 

 Kansas and Nebraska (southern and eastern part only) and the 

 southeastern corner of Wyoming : this is the most advanced 

 point for the genus in a northwesterly direction. Entirely isolated 

 from the range of this group, thus far described, we find a species 

 (C. digueti) in Mexico (Pacific side, State of Jalisco), and another 

 species (C. immunis, known from the prairies of Michigan, Indiana, 

 Illinois, Wisconsin, Iowa) is said to be present near Orizaba, 

 Mexico. 



Therefore we may say, generally, that the centre of this group is 

 situated in the central part of the United States, about in that 

 region where the three large rivers, Missouri, Mississippi and Ohio, 

 unite. Thence it extends into the eastern and southeastern moun- 

 tains, but hardly across them ; northward, it reaches the St. 

 Lawrence and the Saskatchewan rivers and westward Wyoming. 

 In a southwesterly direction it hardly reaches Texas, and the Mexican 

 localities seem to be isolated from the rest. 



Of the three species of the fifth group, two are found in Mexico 

 and one near New Orleans. 



