Maryland Geological Survey 545 



the free surface. On the early whorls the upper outer edge is angulated 

 and bears a row of sharp oblique tubercles, but in final growth this 

 angulation disappears and rounded tubercles are irregularly scattered 

 over the whole surface. 



The species bears much resemblance to Sp. angulatus Hall (15th Ann. 

 Eept. N. Y. State Cab. Nat. Hist., p. 112, 1862) from the Hamilton 

 shales of New York, but while that species is tubercled the growth is often 

 irregular and the later whorls are lax and free. 



Diameter 4 mm. 



Occurrence. — Jennings Formation, Chemung ? Member. On Side- 

 ling Hill Creek, Allegany County. 



Collection. — Maryland Geological Survey. 



Spieorbis sp. 



Description. — Casts of a small Spirorbis have been observed in the 

 Parkhead that do not show exterior ornamentation. Their condition does 

 not permit confident specific determination. 



Occurrence. — Jennings Formation, Parkhead Member. Two miles 

 north of mouth of Town Creek, 1723. 



Collection. — Maryland Geological Survey. 



INCERTAE SAEDIS 



Genus PTERIDICHNITES n, gen. 

 Fern-like imprints consisting of t^vo rows of small pits bordered by a 

 narrow elevated margin and separated by narrow transverse ridges. Pits 

 nearly equidimensional. The nature of these objects is problematical. 

 They are probably tracks of crastaceans or possibly of annelids. The 

 tracks suggest those referred to the genus Nereites, but are not sinuous. 

 (From Pteris a fern, ichnos a track.) 



Pteridichnites biseriatus n. sp. 



Plate XLVI, Fig. 6 



Description. — Imprints consisting of two parallel grooves with raised 

 borders, divided by narrow transverse ridges into shallow, nearly square 

 35 



