406 PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 



coucentrically waved; over the sculpture the shell has a polished ap- 

 pearance; margins thin, sharp; interior smooth, somewhat polished; 

 the scar of the pedal muscle narrow, a considerable distance within the 

 margin, the anterior ends of the scar enlarged, hooked backward on 

 their inner edges ; these ends connected by a line broadly arched for- 

 ward and marking the attachment of the mantle to the shell over the 

 head. Soft parts whitish, dotted with fine purple dots; mantle edge 

 thickened, smooth; muscular base of the foot nearly orbicular, extremely 

 thin and delicate, not high; muzzle short, plam, without any strongly 

 defined margination, with the end finely i^apillose and a little puckered; 

 mouth small, furnished with two lateral pads covered by a cartilaginous 

 thin coat which completely dissolves in liquor potassa', and hence can 

 hardly be termed a jaw, though it occupies the place of the buccal 

 plates in other genera; head moderate, not much produced, broader 

 than long, extended laterally into a single rather short and stout tent- 

 acle ou each side; tentacles showing slight transverse ridges (due to 

 contraction?) destitute of any basal elbow or tubercle, such as bears the 

 eye in allied groups, and with no appearance of any organ of vision or 

 bulbus, whatever. Behind the head a thickened ridge, containing a large 

 vessel, takes origin and jiasses backward around the right' man tie edge, 

 reaching nearly to the posterior median line; from this ridge depend 

 fifty or sixty branchial leaflets resembling those of PateUa, and not like 

 those of Acmcca or the FlssurelUdce ; these leaflets are very large in pro- 

 portion to the size of the animal, and gradually diminish posteriorly; 

 they are slightly inclined outward; the anal papilla is very inconspicu- 

 ous, opening between the line of the branchia and the head, a little to 

 the right of the head; the intestine is much shorter than in the Patel- 

 ltcl(c, and coiled in much the same way through the very large greenish 

 hepatic mass; this surrounds the ovary, which rises to the surface of 

 the back in about its center, and in this individual was crowtied with 

 eggs already in various stages of segmentation and of about the size 

 and general appearance of those of Acmcva patina. The ovary appeared 

 to be a single simple sac-like body of irregular contour as in Acmoia ; 

 no crop was noticed and the stomach seemed of very moderate size. 



Since but one specimen was available the observations were more or 

 less imperfect, especially since the internal parts were somewhat soft- 

 ened. To obviate the extreme contraction caused by alcohol, the speci- 

 men was placed in water with the result that it almost immediately 

 swelled and became covered with an immense quantity of very slimy 

 mucus, which rendered it almost impossible to handle, being so slippery, 

 and it had to be replaced in alcohol again to harden before the exam- 

 ination could proceed. The edge of the mantle is marginated with a 

 rather broad thickened band, apparently without papilltB or other ap- 

 pendages of any kind. The space occupied by the branchiae is so large 

 that the remainder of the animal is forced a good deal to the left in the 

 ai)erture of the shell. 



