CAEB0NIFEE0US SYSTEM. 239 



Fossils. None of the strata of the Lower coal-measures of 

 Iowa are usually found containing many fossils, but such 

 animal remains as have been thus far discovered among 

 them are without exception of marine origin. Judging from 

 their analogy with existing species which inhabit salt water, 

 they are supposed to have existed in shallow seas and 

 estuaries. 



Yeetebeates. This sub-kingdom is, so far as jet dis- 

 covered, represented only by the remains of fishes, and these 

 belong to both the orders, Selachians and Ganoids. These 

 remains consist of the dermal plates, teeth, and spines of the 

 last named order, and thus far of the teeth only of Selachians. 

 They are all rare and are mostly confined to the dark carbon- 

 aceous shales. The spines referred to the Ganoid order with 

 some doubt, are rather small, flattened, and have a somewhat 

 bushy extremity. They are found associated with the teeth 

 of the genus Petrodus, no other fish remains being found 

 immediately associated with them. They have thus far been 

 found only in the dark colored laminated carbonaceous 

 shales. Associated with these spines and teeth in the shales 

 are often found compressed globular or ovoid lumps, from 

 half an inch to an inch in diameter, with a dull gray color 

 upon fracture. These are, doubtless, the fossilized excrement 

 of the same fishes, analysis showing them to contain much 

 phosphate of lime. 



Articulates. The only remains of Articulates thus far 

 discovered in the Lower coal-measure strata of Iowa, are a 

 few incomplete specimens belonging to the Trilobite genus 

 Pliillipsia, which are very rare. It is likely that ostracoid 

 crustaceas also exist in these strata as they do in those of 

 the Upper and Middle coal-measures. Possibly insects also 

 exist among them as they are known to do in their equiva- 

 lents in Illinois. 



Mollusks. These are represented by remains belonging 

 to the classes Cephalopoda, Gasteropoda, Lamellibranchiata, 

 Brachiopoda, and Polyzoa. Ceplialopods are rare; one small 

 species of Orthoceras only being yet discovered. Gasteropods 



