AET.'s NEW FOSSIL MUSSELS FROM PERU MARSHALL 5- 



nearly straight posterior to the beak and sloping downward to the 

 posterior margin. Anterior to the beak the very short dorsal de- 

 scends rapidly to meet the anterior margin. Ventral margin nearly 

 regularly curved, sweeping into the anterior margin in a broad curve 

 and not differentiated from it. Posteriorly the shell becomes nar- 

 rower, the ventral margin curving sharply to join the posterior mar- 

 gin, the two margins differentiated from each other by the end of 

 the posterior ridge. Posterior ridge well marked, with an indistinct 

 rib running along its summit. Posterior area with two faint radiat- 

 ing grooves forming a low, broad rib between them. General surface 

 of shell rather smooth, concentric growth lines not well marked except 

 on the posterior area and near the anterior margin. At the anterior 

 end of ventral margin are five short radiating flutings. A faint 

 groove just appreciable to touch and made faintly visible by a dark 

 line extends from the beak to the ventral margin just behind its 

 middle point, probably marking the depth to which the animal in- 

 serted itself into the material of the bottom. Interior pearly, ante- 

 rior adductor scar deep, posterior scar well marked but shallow. 

 Pallial line well marked, about 6 mm, from the ventral margin. 

 Umbonal area very prominent because of the strong radial sculptur- 

 ing. At the anterior end this sculpture consists of five fine, rather 

 granular, curving sharp threads, the middle area shows a crudely 

 V-shaped arrangement, partly broken up into stout nodules. The 

 posterior portion has several direct radiating threads or riblets. 



The type (Cat. No. 370812, U.S.N.M.) measures: Length, 64 mm.; 

 height, about 30 mm. ; diameter if both valves were present would be 

 about 16 mm. It was collected by Doctor Singewald at Pebas, Peru, 

 and is named in honor of Dr. Julia A. Gardner, of the United States 

 Geological Survey. Cat. No. 370814 includes a cast, a partially 

 preserved umbonal portion, and a number of fragments, all from 

 the type locality. Several partially preserved specimens were re- 

 turned to Professor Singewald. 



The type, owing to a rich chestnut coloring due to a ferruginous 

 stain, has almost the appearance of a recent shell. The species is 

 not closely related to any known recent species. In boldness and 

 extent of umbonal sculpture it is scarcely equaled by any recent spe- 

 cies, and in the breaking up of part of the sculpture into nodules it 

 stands unique. 



EODIPLODON PEBASENSIS,- new species 



Plate 1, figs. 5, 7 



Shell apparently rather compressed, thick, rounded in front, 

 obliquely truncated behind. Dorsal margin lightly arched, ventral 

 margin slightly curved, meeting the f)Osterior margin in an obtuse 

 angle, and rounding into the anterior margin. Posterior ridge low 



