CONTEIB0TIONS TO PALiEONTOLOGT. 221 



SUPPLEMENTARY NOTE 



OX SOME FOSSILS OF THE LOWER BEDS OF THE POTSDAM SANDSTONE 

 OF THE UPPER MISSISSIPPI VALLEY. 



SiNCK the completion of the printing and engraving of the plates 

 relating to the fossils of the sandstone of tlie Upper Mississippi 

 valley, a re-examination of some of the specimens from the lower 

 beds near Trempaleau, by Mr. Whitfield, has brought to light 

 several forms, quite new and distinct from any before noticed*. 

 One of them, a Crustacean somewhat resembling the pygidium of 

 a Trilobite, has a very narrow axis and large swollen lateral lobes. 

 It differs from the p} gidium of a trilobite, in the extension of the 

 narrow axis quite to the margin of the sliield. On thestraiglit side, 

 the articulating face (if such it be) difters essentially from the 

 corresponding parts of a trilobite. In these respects, also, it dilfers 

 from Agnostus. 



From its remarkable characters, it seems necessary to designate 

 it as an undescribed generic form ; and I propose the name Pem- 



PHIGASPIS. 



GENUS PEMPIIIGASPIS ( n. g.). 



Generic characters. The general form of the part cf the shield 

 known is semielliptical, rounded behind, neaily straight in the 

 middle in front, and becoming rounded towards the outer mar- 

 gin : distinctly trilobate. Axis narrow, straight, and slightly 

 narrowing posteriorly; distinctly annulated : annulations di- 

 rect. Lateral lobes ovate, extremely gibbous or ventricose, rising 

 much above the axis : margins at the sides abruptly incurved. 



PEMPHIGASPIS BULLATA (n.s.). 



PLATE V A. FIGS. 3, 4 & 5. 



Three individuals of this species have been examined : the largest is 

 about one-fifth of an inch in width, and a little less in length; The axis is 

 marked by seven annulations, besides the posterior one : the lateral lobes 

 are smooth, ovate, and very ventricose. The anterior extremity of the middle 

 lobe, with a small area on the inner anterior face of the lateral lobes, may 

 have been articulating faces. The lateral margins are abruptly incurved, 

 flat below, with a narrow elevated ridge just without the inner edge. 



The specimens are casts of the interior, and the character of the exterior 

 surface is unknown. The figures are six times enlarged. 



Fxa. 3. Tlie upper surface. Fig. 4. The lower surface. 



Fig. 5. A profile view from the posterior extremity. 



GENUS AMPHION? 



A single glabella, much resembling in its lateral lobes the gla- 

 bella of a Calymene, has been found in a specimen from the lower 

 beds near Trempaleau. 



Although not entirely corresponding with Amphion, I refer it, 

 for the present, to that genus. 



* Several of these are illustrated on Plate v a, tigs. 3-7. 



