6- PROCEEDINGS OF THE NATIONAL MUSEUM vol. 74^ 



and not well pronounced. Beak set well forward, about 5 mm. 

 from anterior edge and 20 mm. from posterior end. Concentric 

 sculpture of faint growth lines. Umbonal region boldly sculptured 

 with radiating ribs and nodules. The anterior portion has five direct, 

 sharp, faintly granulate radiating threads. The middle portion has 

 the riblets arranged in V pattern and somewhat nodulous. The pos- 

 terior portion has four sharp, direct slender threads. Pseudocardinal 

 tooth stout. 



The type (Cat. No. 370813, U.S.N.M.) is a fragment but includes 

 all the shell up to a well-marked rest period. At that period it meas- 

 ured : Length, 25 mm. ; height, 13 mm. It came from Pebas, Peru, 

 and was collected by Dr. Joseph T. Singewald. 



In beak sculpture this species resembles and might be mistaken 

 for Eodiplodon gardnerae^ but careful examination shows marked 

 differences. In form the two species are very different, Eodiflodon 

 gardnerae being very elongate, narrow, and rather inflated, while 

 Eodiflodon pebasensis is subquadrate, broad, especially at the pos- 

 terior end, and rather compressed. 



ANODONTITES? 



Included with the collection sent by Doctor SingeAvald are ?ome 

 fragments of a very large fossil pearly fresh-water mussel, from 

 Tarapoto, Peru. Cat. No. 370815. There is not enough left to 

 determine the genus, but what we know of the microscopic structure 

 of the South American Naiades leads to the belief that they belong 

 to some genus in the subfamily Mutelinae of the family Mutelidae. 

 The shell must have been very large and massive, as one of the 

 fragments from along the ventral margin has a thickness of about 

 8 mm., and the pallial line is about 27 mm. from the ventral edge. 

 These measurements are not equaled by any known South American 

 Naiad, recent or fossil. They call to mind the size and massive- 

 ness of our largest North American Naiades, namely, the genus 

 Crenodonta. The numerous layers of nacreous material, eacli very 

 thin, between the pallial line and ventral margin indicate that the 

 shell was aged, and that growth at this period was very slow. Dur- 

 ing this time the pallial line appears to have remained nearly sta- 

 tionary. The prismatic layer is very thick (in some places about 

 a millimeter) indicating a member of the Mutelinae and not the 

 Hyriinae, as in the latter the layer is thin and usually flakes off 

 with the periostracum. In spots the component spicules of the 

 prismatic layer have separated from each other and lie scattered 

 about or in a heap. 



