356 



Annals of the Carnegie Museum. 



mantle in front of the branchial is also somewhat distant from the 

 toothed outer edge, and bears four to ten, rather distant, subconical, 

 small papillae, which are smaller than the papillae of the branchial, 

 and decrease in size forward. Along this part of the edge runs a 

 black streak, and the papillae also are black or brown. The space 

 between the two edges is blackish-brown, lighter toward the outer 

 edge. Before the middle of the lower margin is reached, the two edges 

 approach each other, and thence forward are normal, the inner one 

 smooth. In the male, the two edges are subparallel and close together, 

 as is normal, and there are only a few small papillae in front of the 

 branchial. 



Posterior margins of palpi connected at base only. Gills and dia- 

 phragm of normal structure. Inner lamina of inner gills entirely 

 connected with abdominal sac. 



Marsupium formed by over half of the posterior part of the outer 

 gill, with hardly any non-marsupial part behind, greatly swollen, 



kidney-shaped, higher in front 

 S3. than behind, and slightly de- 



formed to suit the shape of the 

 shell, presenting a broad face 

 outwardly and downwardly, and 

 having a blunt edge toward the 

 median line of the animal, where 

 the two marsupia come into 

 contact. Margin of marsupium 

 without pigment. Ovisacs nu- 

 merous, thirty to forty. Glo- 

 chidium of medium size, almost 

 semicircular; length and height 

 0.21 mm. (See Ortmann, 1911&, 

 pi. 89, fig. 24; Lea's figure, Obs., VI, 1858, pi. 5, fig. 19, is not correct.) 

 Color of soft parts whitish. Margin of the mantle with black spots 

 in the posterior parts, black inside of the branchial opening, and with 

 black streak in front of the latter, farther in front brown. 



The characteristic structure of the inner edge of the mantle is very 

 poorly developed in this species, and if it were not for the other 

 species, its significance would hardly be realized. Nevertheless, 

 according to shell characters, this is a true Truncilla (being besides 

 the type). 



mp 



Fig. 27. Truncilla triquetra Rafines- 

 que. Gravid female, from Allegheny 

 River, Aladdin, Armstrong Co., Pa. 

 (Cam. Mus., No. 61, 3,358.) Coll. Sept. 

 18, 1908. 



