592 MEMOIRS OF THE CARNEGIE MUSEUM. 



end of the slicll, which is more elevated above the base-hne, and in the more curved 

 ventral margin. The sculpture of this species undoubtedly is similar, but the 

 details have not been described. 



Simpson says that this species is very variable in sculpture. However, I 

 find that my specimens (twenty at hand) are rather uniform in this respect. Only 

 in the youngest specimen is the subradial sculpture of the posterior part not so 

 well develojKKl; but in the second (37 mm. long) it is distinctly seen. 



There is a good deal of variation in the shape of the posterior end, and the 

 posterior margin may be more oblique or may be more vertical in its lower part. 

 Very often the nearly vertical truncation of the posterior end produces the ap- 

 pearance of a biangulation, chiefly when the faint groove of the posterior slope is 

 visible. 



Anatomy. — Soft parts of six males and four barren females at hand for study. 

 Anal opening separated from the branchial by a mantle connection, open and 

 nowhere closed, its inner edge smooth or nearly so. Branchial opening with fine 

 papillae. Paljii longer than high, lower margins convex, posteriorly truncated, 

 the truncation forming the short posterior margins, which are connected at base 

 only. 



Gills of medium width, the inner the wider anteriorly, its anterior end im- 

 mediately behind the palpi, and attached to the whole interval between the palpi 

 and the anterior end of the outer gill. The latter at the highest point of the mantle- 

 attachment-line. Inner lamina of inner gill entirely connected with abdominal 

 sac. 



Gills with well developed septa. In the non-marsupial gills the septa are 

 irregularly alternating, stronger and weaker. In the female the inner gill is ?nar- 

 supial for nearly its whole length, with stronger and more uniform, but not more 

 crowded, septa. The septa possess the usual swelling, forming vertical ridges 

 projecting into the lumen of the water-tubes, dividing the latter into an inner 

 compartment (ovisac), and an outer (secondary water-tube). 



49. Anodontites TENEBRicosA (Lea) (1834). 



Anodonta tenehricosa Lea, Obs., I, 1834, PL 12, fig. 30; D'Orbigny, 1843, p. 616. 

 Anodon tenebrosa Sowerby, XVII, 1807, PI. 13, fig. 43. 

 Aiiodon tenehricosa Sowerby, XVII, 1870, PL 31, fig. 123. 

 Anodonta tenebricosta Corsi, 1901, p. 457, fig. 58. 



Glabaris tenehricosa Von Ihering, 1893, p. 01; Nehring, 1893, p. 103; Simpson 

 1900, p. 930. 



