662 Systematic PALi-oxToi.ociv — Upper Devonian' 



conspicuous and (loiuinale the rcvolvinu- stri;v. In nearly all the s])eci- 

 mens there is a distinct alternation in the strength of the revolving lines, 

 and the finer ones hecome obsolete." Hall, 1879. 



Length 22 nun.: diani. 20 nun. 



Excellently preserved and characteristic specimens of this recurrent 

 Hamilton species are present in the Parkhead. It may he readily recog- 

 nized by its sculpture and by the revolving peri})heral hand characteristic 

 of this genus. 



Occurrence. — Jennings Formation, Parkhead Member. Pocky 

 Bun ?; Town Creek, 1863; 2 miles west of Pawpaw, 1493 common; 2Vi> 

 miles above mouth of Sideling Hill Creek. 



CoIIertion. — Maryland Geological Survey. 



Pleurotomaiua ? sp. 



Description. — A greatly compressed individual found at Ellerslie, 

 Pennsylvania, is doubtfully referred to this genus. It is not sufficiently 

 well preserved to permit illustration. 



Occurrence. — Jennings Formation, Chemung ■Member. Ellerslie, 

 Pennsylvania, i;51G. 



Collection. — Maryland Geological Survey. 



Genus MURCHISONIA d'Archiac and de Vemeui! 

 The genus Murchisonia was formerly made to contain species of many 

 distinct generic types. Further study of these forms has shown that it is 

 desirable to separate them into a numljer of distinct genera upon the basis 

 of their exterior ornamentation and internal structure. Two of these 

 genera are present in the Jennings fauna, Hormotorna and J'Jcloiiiariu. 



Murchisonia ? sp. 



Description. — A large species of this genus is found with some fre- 

 quency in the form of external casts but in no instance are the specimens 

 so preserved as to justify an attempt at their identification. These shells 

 attain a length of oO-M mm. with a basal width of 1"?-14 mm. and luive 

 7-8 whorls. 



