116 Morgan Expeditions. 



precludes its being placed in the genus Pleurotomaria, to 

 which it might seem to be related from the shape and appear- 

 ance of the internal mould alone. 



Very abundant in the Devonian sandstone of Erere, Prov. 

 of Para, Brazil ; associated with Spirijera Pedroana, JSfucu- 

 lites Nyssa, etc. 



Dedicated to Mr. Furman of Para, a gentleman to whom 

 both expeditions are deeply indebted. 



Genus PLATYCERAS, Conracl. 

 Platyceras symmetricum. 



Platyceras symmetricum, Hall. 15lh. Aun. Rep. St. Cab., N. Y., 1862, p. 

 34. 



Description of the Erere form: — Shell small, argonautiform iu side 

 view, very slightly elongated and somewhat laterally compressed. From 

 the apex, which is minute and twisted very slightly to the right of the 

 median line, the shell increases very rapidly in size, the ventral side of 

 the body volution passing tangentically for a short distance beyond the 

 last preceding volution. Volutions about one and one-half in number, 

 the outer one, small and much compressed where it commences, but be- 

 coming gradually less compressed and more fully rounded toward the 

 aperture, enlarging rapidly at the same time. The aperture is oval in out- 

 line, with the sinistro-dextral diameter a little less than the dorso-ventral. 

 The margin is apparently sinuous, but is defective in the specimen. Exte- 

 rior surface of shell not preserved. Surface of internal mould of body 

 volution not very irregular, somewhat rugose and traversed near the front 

 by numerous, rather indistinct growth lines, which bear on each side a few 

 deep, rounded flexures. To these flexures a few short, irregular, longitu- 

 dinal undulations near the aperture appear to correspond. There is a 

 slight prominence, probably the impression of the base of a spine, just on 

 the left of the dorsal line, midway between the aperture and the beginning 

 of the outer volution. Dimensions : greatest length from anterior mar- 

 gin of aperture, 19 mm ; dorso-ventral diameter of aperture, 13.5 mm ; 

 sinistro-dextral diameter of same, 12 mm . 



Only one specimen of Platyceras, the one described above, 

 was obtained from Erere. It agrees with P. symmetricum 

 of Hall, Hamilton group, N. Y., in being symmetrical and 

 in having the same number and character of volutions ; but 

 it is much smaller than any specimen of P. symmetricum 

 from the Hamilton group which we have seen, and more per- 



