Maryland Geological Suevey 297 



the Devonian Platycera in the following language: "In the Devonian 

 the phylogerontic [old aged] noncoiling Platycera abound. We find all 

 degrees of coiling, from the close-coiled nonumbilicate Diaphorostoma, 

 which appears with slight modifications throughout most of the series, to 

 the straight ' Orthonyehia,' which appears as a terminal member in most 

 groups. Very often a number of species of ' Platyceras ' can be traced to 

 a species of Diaphorostoma or Strophostylus occurring with them, the 

 gradations being perfect. From such evidence it appears that the numer- 

 ous species classed together as Platyceras must be split up into groups, 

 each of which has been derived from a close-coiled ancestral species, prob- 

 ably within the same geological horizon. If so, the name Platyceras 

 becomes meaningless for generic purposes. The great difficulty which 

 besets the proper breaking up of what appears most certainly to be a 

 group of polyphyletic origin lies in the small number of ornamental 

 characters which can be made use of in tracing out relationships." ' 



Length of largest specimen, more than 23 mm.; diameter from post- 

 erior to anterior side of aperture, 11 mm. or more. 



Occurrence. — Eomney Formation, Hamilton Member. On Han- 

 cock-Harrisonville Road about 2 miles north of Hancock. 



Collection. — Maryland Geological Survey. 



Platyceras cf. syimmetricuim Hall 

 Plate XXXYII, Fig. G 



Description. — A single poorly preserved, exfoliated specimen which 

 is incurved nearly in the same plane, the body-whorl expanded rapidly 

 toward the front and about equally on each side of the dorsum while the 

 surface shows obscure longitudinal ridges. The specimen was sent to Dr. 

 Grabau who reported as follows : " I think no two Platycera ever agree. 

 This comes nearest to P. symmctricvm it seems to me." 



Length, about 27 mm.; transverse diameter of aperture, about 25 mm. 



' Am. Nat., vol xxxvi, Dec. 1902, p. 939. 



