242 



Annals of the Carnegie Museum. 



ciduous, often absent, sometimes torn. Branchial opening with 

 papillae on inner edge, anal with distinct, but small papillae. Palpi 

 subfalciform, pointed behind, their posterior margins connected for 

 about one-third to one-half of their length. 



mp 



Fig. 4. Fusconaja vubiginosa (Lea). Male, from South Fork of Tenmile Creek, 

 Waynesburg, Greene Co., Pa. (Cam. Mus., No. 61, 4,509.) Coll. May 6, 1910. 



Gills short and rather wide, with curved lower margins (correspond- 

 ing to the shape of the shell), the inner gill wider. Outer gill attached 

 at its anterior end at the highest point of the attachment-line of the 



mantle, far above the palpi; in- 

 ner gill with its anterior end 

 slightly in front and below that 

 of the outer gill, widely separated 

 mp from the palpi. Outer lamina 

 of outer gills entirely connected 

 with the mantle. Inner lamina 

 of the inner gill free from the 

 abdominal sac, except at its an- 

 terior end. Behind the foot, the 

 two inner laminae of the inner 

 gills are connected up to their 

 posterior end. Thus a complete gill-diaphragm is formed, which 

 reaches backward close to the posterior margin of the mantle. 



Both gills possess well developed septa and water-tubes, running 

 parallel to the gill-filaments. In the male, the septa are rather distant 

 and the water-tubes are wide. The septa are merely lines of con- 

 nection of the interlaminar tissue. In the female, all four gills are 

 marsupial, the septa are better developed, thicker and longer (in the 



Fig. 4a. Left gills of a sterile female from 

 same locality. 



