SILURIAN FOSSILS 



73 



Calliocrinus has a cup that tapers to a point on top. It has more 

 than 13 plates and a rounded triangular outline. It occurs in the Cedarville 

 ville. 



Habrocrinus benedicti (fig. 145) has conspicuous arm bases that pro- 

 ject sideways. The plates are convex but have a depression in the center 

 of each one. It is found in the Cedarville and Guelph. 



Marsupiocrinus praematurus ( Marsipocrinus in older publications) 

 has conspicuous arm bases (fig. 146). The plates are flat and striated 

 from the center outward. It occurs in the Cedarville and 

 Guelph. 



In Periechocrinites (fig. 147) the shape of the cup may 

 be elongated or globular, hence it is keyed under both 

 groups. The cup is flat on top, the arm bases are promi- 

 nent, and the plates are flat and plain. _P_. tennesseensis 

 occurs in the Cedarville. 



E ucalyptocrinites (E ucalyptocr inus in older publications) has arm 

 bases but they do not project sideways. The plates are flat or slightly 

 convex, the body conical, not globe-shaped as in the next two genera. 

 Eucalyptocrinus crassus (fig. 148) is found in the Niagaran. 



Lecanocrinus has inconspicuous arm bases, a globe-shaped cup, 

 and flat plates. It is larger than Pisocrinus, being always more than 

 3/4 inch in diameter. Lecanocrinus waukom a (fig. 149) is found in the 

 Cedarville and Guelph. 



Pisocrinus is like Lecanocrinus but smaller - always less than 

 3/4 inch in diameter. _P. gemmiformis occurs in the Lower Niagaran. 



Fig. 145 



Fig. 146 



Fig. 147 



Fig. 149 



Fig. 14fi 



Books for further study 



Bassler's (1915) index lists all Ordovician and Silurian species known to that date; it is 

 useful in locating descriptions and figures, especially of the rarer species. Meek (1873) and 

 Hall and Whitfield (1875) describe and figure many of our Silurian species. Several Indiana 

 Geological Survey reports (see especially Kindle and Breger, 1904) have descriptions and fig- 

 ures of Silurian species which are found in Ohio as well as in Indiana. Many of our Silurian 

 species were first described in Canada. The works of Billings (1865) and of Whiteaves (1906) 

 are particularly helpful but they are rare and have long been out of print. 



