6 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.61. 



nence behind, both with the edge creniilated. Nacre white, pearly, 

 but not very iridescent. 



The type (Cat. No. 335770, U.S.N.M.) measures: Length 55 mm., 

 height 33 mm., diameter 21 mm. It is one of a lot of four specimens 

 from Arroyo Bellaco, Department of Paysandu, Uruguay. Cat. No. 

 340887 includes another specimen from the same locality. Cat. No. 

 340886 includes one specimen from the Uruguay River at Paysandu. 

 Cat. No. 335771 includes one specimen from Arroyo la Boyado, De- 

 partment of San Jose, and Cat. No. 335772 Includes a single valve 

 from Arroyo Canelon Chico, Department of Canelones, Uruguay. 

 All the specimens were received from Dr. Florentino Felippone of 

 Montevideo. 



As the name indicates, this species is closely related to Diplodon 

 trivialis Simpson, from which it differs chiefly in the character of 

 the umbos. Fortunately the sculpture of the beaks of the types of 

 both trivialis and trivioloides is sufficiently well preserved to show 

 that they differ markedly, the sculpture of the former being fine 

 radial threadlike raised lines, while the sculpture of the latter con- 

 sists of coarse radial ribs. Trivioloides is also closely related to 

 peculiaris Lea, from which it differs in form and in character of 

 periostracum. The four specimens in the type lot are remarkably 

 uniform in all details and any one might have served as the type. 



In the natural condition of the shell the division into two areas of 

 color is not very striking; but if the shell be cleaned with oxalic 

 acid, this characteristic becomes one of the most noticeable features 

 of the species. 



ANODONTITES PITTIERI, new species. 



Plate 1, figs. 9, 11 ; plate 2, figs. 9, 12 ; plate 3, fig. G. 

 Shell high, roundly subquadrate, compressed, rather thin, slightly 

 thicker at the middle than at the ends. Valves closed all round. Con- 

 vexity nearly equally rounded, without a clearly defined posterior 

 ridge, with several obsolete radiating ribs on the posterior dorsal area, 

 these ribs with faint indications of green coloring. Anterior portion 

 of surface vernicose. Posterior portion dull and much roughened 

 by concentric lamellae of periostracum. Middle portion with several 

 radiating, faintly impressed lines and several radiating rufflings of 

 the periostracum. Principal rest periods six, indicated by dark con- 

 centric lines. Vicinity of the beaks flesh color, rest of shell dark 

 straw color, deepening to light chestnut in front. Nacre pinkish and 

 slightly pearly, in the cavity of the shell, brilliantly iridescent at the 

 adductor scars and in a band just above the prismatic border. In- 

 terior everywhere finely radiately striated except on the prismatic 

 borders. All adductor scars superficial, not appreciable to touch. 

 Prismatic border very broad, occupying one-seventh of the height of 



