64 



OHIO FOSSILS 



Fig. 101 



Nucleospira (fig. 101) is a wide little shell whose surface is covered with 

 short spines, though they are not always preserved. Two species are common 

 in some parts of the Niagaran. 



Meristina maria (fig. 102) is much like Nucleo- 



spira but larger and rounder and the margin away from 

 the beak has a small notch in it. It is abundant in the Niagaran. 



The genus Leptaena (see fig. 59) is found from the Ordovician to 

 the Mississippian in Ohio. Leptaena rhomboidalis is the Silurian species. 

 It is unmistakable for it is the only Silurian one in which the combination 

 of strong concentric ridges and a sharp downbending of the shell canbe 

 found. The latter feature distinguishes it from the next species. It is 

 common in the Niagaran. 



Fig. 102 



Fig. 103 



Plectodonta transversalis ( Plectambonites in older publications) is like 

 Leptaena but the shell is not bent downward at the margin (see fig. 60). It is 

 common in the Dayton and Euphemia. 



Crispella crispa (Spirifer crispus in older publications) is one of a num- 

 ber of species whose shells suggest butterfly wings. Shells of this type are 

 called spiriferoid, that is, Spirifer-like. They were once all lumped together 

 in one genus, Spirifer , but it was later found that the internal structures were 

 very different in groups of species so they were split up among a dozen or so 

 genera. Crispella crispa (fig. 103) canbe distinguished 

 from the other Silurian spiriferoids by its concentric lamel- 

 lae which bear small spines. It is common in the Niagaran. 



Another spiriferoid, Platystrophia ( see fig. 62 ) is 

 abundant in the Upper Ordovician and represented by a few 

 Silurian species. It may be distinguished from Crispella 

 by its weaker, not leaf-like concentric ornamentation. 



Gypidula galeata (fig. 104) has a short hinge line 

 and its radiating ornamentation consists of only a few 

 folds. The width and height of the shell are almost equal 

 and it is a much smaller species than Pentamerus laevis 

 with which it might possibly be confused. It is common 

 in the Niagaran. 



Pentamerus laevis (P. oblongus_ in older publica- 

 tions) is the largest of our Silurian brachiopods (fig. 105), 

 up to 5 inches long, and adult specimens are unmistaka- 

 ble. The width is always much less than the height, a 

 feature which helps separate the genus from Gypidula. 

 P. laevis is common in the Niagaran. 



Rhynchotreta is one of several genera of small 

 brachiopods with distinct sinus and fold. It has a decid- 

 edly triangular outline, the beak forming one point of the 

 triangle and the opposite margin of the shell the other 

 two. Before identifying a specimen with this genus, the 

 figure for Stegerhynchus should be studied also. Rhyn - 

 chotreta americana (fig. 106) is abundant in the Niagaran. 



Stegerhynchus (fig. 107) is similar to Rhynchotreta 

 but. has a rounder outline. It differs from Anastrophia , 

 Uncinulus , and Homoeospira in having a decidedly pointed. 



Fig. 105 



