REPORT OP THE STATE PALEONTOLOGIST 1902 108o 



tions during which 2 feet of light yellowish impure limestone, 

 showing on the weathered surface casts of a very finely branch- 

 ing organism, probably a plant, were formed. On this rests a 

 greenish shaly marlite, the basal stratum of the Salina. The 

 next layer consists of a bench of Waterlime marked by shrink- 

 age cracks, indicating a temporary exposure to the air during 

 the time of formation. 



It is thus seen that preparatory, as it were, to the coming 

 of the Salina fauna, there was a marked change in physical 

 conditions. The shallowing of the sea, with a probable increase 

 of salinity and turbidity of the waters, probably had more than 

 anything else to do with the displacing of the Niagara fauna. 

 While these changes were going on, the first of the Salina 

 fauna, a Pterinea, a little more rhomboid and convex than 

 P. emacerata of the Rochester shale, appeared. Later, in 

 the waterlime bench, besides the Pterinea, a Lingula, a 

 Leperditia (L. scalaris), and also an Orthoceras, occur. 

 With the exception of the last, which has not been noted else- 

 where in this section, these fossils make their next appearance 

 in the black shale, where they are accompanied by the 

 eurypterids. 



The eurypterids are by no means uniformly distributed 

 throughout this shale. The species representing the new genus 

 to be described, occurs most abundantly in the lower half, 

 where it is so prolific that certain planes are literally packed 

 with its remains, making this probably the richest eurypterid 

 stratum known. The genus Eurypterus, represented by a single 

 large species, occurs most frequently in the upper half of this 

 black shale, just above the 2 inch limestone parting. The Ptery- 

 gotus head [pi. 24, fig. 7] was also found in the upper portion. 



The dolomite layers associated with this black shale are 

 marked by an almost complete absence of eurypterids, the 

 Leperditia and Pterinea, with the exception of an occasional 

 specimen of a small pentalabiate Gomphoceras of character- 

 istic Siluric type, being the only forms found in them. From 

 the fact that the occupation of the area by the merostome fauna 

 followed one of these dolomite-forming intervals, was twice 



