292 Annals of the Carnegie Museum. 



Soft parts and glochidia described by Lea (Obs., VIII, i860, p. 373). 



I think my specimens belong to this species, although they are all 

 remarkably shortened and truncated posteriorly. They are all 

 gravid, with glochidia. Possibly this species also is hermaphroditic. 



Soft parts absolutely identical with those of A. inibecillis, and 

 the glochidia also are practically identical. Length 0.29; height 

 0.30 mm. (The difference from the measurements given for A. 

 imbcciUis may be due to the personal equation of the observer.) The 

 shell of this species reveals that it undoubtedly belongs to the same 

 group as A. imbecillis. 



Anodonta grandis Say. 



Numerous specimens of the typical form as well as of several vari- 

 eties have been investigated. They come from western Pennsylvania, 

 Kansas, northern Alabama, and Louisiana. 



The breeding season begins in August and September, and ends 

 very early in spring, for in April the majority of the females have 

 already discharged their glochidia. But occasionally gravid females 

 are found as late as the end of May (latest date, May 22). 



The soft parts have been described (as of A. plana, decora, ovata) 

 by Lea (Obs., X, 1863, p. 452) and by Simpson (in Baker, 1898, p. 52, 

 chiefly as to color). 



Mantle-connection between anal and supra-anal very long, anal 

 small, its inner edge crenulated. Branchial opening with papillae, inner 

 edge in front of branchial smooth. Posterior margins of palpi con- 

 nected for one-third to one-half of their length. Anterior end of inner 

 gills midway between that of the outer gills and the palpi, so that it is 

 widely remote from the palpi. Diaphragm normal. Inner lamina 

 of inner gills free except at anterior end. Septa of the gills distant 

 in the male and the non-marsupial gills of the female. Marsupium 

 formed by the outer gills, which swell greatly when charged, distending 

 at the edges so as to appear truncated, and developing lateral water- 

 tubes, while the ova are contained in the central ovisacs; the latter 

 are not subdivided. No placenta? are formed, and the glochidia are 

 discharged loose, in irregular masses. 



Glochidia very large, the largest known to me, even larger than those 

 of A. cygnea, subtriangular, slightly higher than long (length 0.36; 

 height 0.37 mm.) with hooks. The glochidia figured by Lea (Obs., 

 VI, 1858, pi. 5, figs. 32-34) as of A. lewisi, ovata, decora, differ some- 

 what from each other, while they actually should be all alike. 



