.Monograph of the Crustacea of the Cincinnati Group. 115 



Feet. 



6th. Triassic and Jurassic 3,000 



7th. Cretaceous : 4,000 



8th. Tertiary , 3,Ooo 



9th. Post Tertiary 1,000 



Total thickness 141,000 



This is about twenty-six miles and seven tenths. When the country 

 is more closely surveyed by geologists, a few thousand feet will pro- 

 bably be added to this column. 



. Monograph of the Crustacea of the Cincinnati Group. (By S. A. Miller.) 



Every collector of fossils in the Cincinnati Group, and every student 

 of its paleontology will bear testimony to the great difficulty ex- 

 perienced in finding either the specific or generic descriptions of fossils, 

 both of which are necessary, in order to become reasonably satisfied of 

 the correctness of the names by which they are known, or to become 

 acquainted with the information and labors of our predecessors, or to 

 acquire any definite knowledge of the science. Many of the generic 

 descriptions, and some of the specific, have never appeared in any 

 American publication, and both the home and foreign descriptions are 

 so dispersed among scientific publications, that it requires a library 

 worth several thousand dollars to contain them all. To obviate this 

 difficulty in part, I have compiled the following monograj)h of the 

 CLASS CRUSTACEA. The characters of the class, the orders, and 

 the families are nearly all copied from British Paleozoic Rocks, by 

 ]\IcCoy, as are also some of the generic and specific characters. Other 

 generic and specific descriptions are from the works of Green, Hall, 

 Meek, Jones, etc. I have added only one new species, Leperdiiia 

 Bxjrnesi, and the description of only a few heretofoi-e unknown parts, 

 but I have pointed out the localities and the range of several species 

 which may have a scientific value, and be of some assistance to col- 

 lectors. Nor do I regard the tracks (fig. 11), for the first time 

 figured as of slight importance. If they are tracks, and I think there 

 can be no reasonable doubt of it, they are most likely those of a crus- 

 tacean, and, if so, probably those of an Asaphus. 



Burmeister Avas of the opinion that trilobites must have possessed 

 tender, soft feet, which were not used to creep about the bottom of 

 the ocean, but were used only in swimming. That they swam in an 

 inverted position, close beneath the surface of the water, the belly 



