GENUS NEBELA— NEBELA CAKINATA. 155 



moist sphagnum of the cedar swamp of Absecom, New Jersey, and I have 

 obtained it from sphagnum bordering a spring in the vicinity of Swai-th- 

 more College, Delaware County, Pennsylvania, but have rarely found it 

 elsewhere. It is usually larger than Nebela coUaris, with which it is found 

 associated, and which it closely resembles in shape and constitution. 



The shell is transparent and colorless, and is compressed pyriform, 

 usually being provided with a more or less distinct neck of variable length. 

 From that of Nebela coUaris it differs in the possession of a well-marked 

 keel, extending from the lateral borders and fundus, and usually commenc- 

 ing about one third the length of the shell above the mouth. The keel is 

 commonly of considerable depth, but is not proportioned in extent to the 

 size of the shell. It is a thin membrane terminating by a sharp free edge, 

 and by transmitted light is defined from the cavity of the shell by the 

 double contour-line of the wall of the latter. It usually presents a more or 

 less indistinctly granular aspect, but not the defined elements of structure 

 of the shell, of which it is an expansion, excepting occasionally obscure 

 traces of the same may be detected. In the transverse section of the shell, 

 which is oval, the keel appears as acuminate points to the poles. 



The mouth of the shell is transversely oval and convex downward, 

 as in N. coUaris. 



The structure of the shell exhibits the same form, variety, and arrange- 

 ment of elements — round and oval disks, narrow rectangular plates, and 

 broader angular plates, as in Nebela coUaris. 



In a single instance, I observed a specimen, represented in fig. 4, in 

 which some comparatively large quartz particles adhered to the shell, scat- 

 tered on the fundus, and especially along the border from which emanated 

 the carina. 



As before mentioned, Nebela carinata is larger than N coUaris, and its 

 range of size is not so great as in this. In twenty specimens measured at 

 different times, six were f ^th of an inch long, five were longer, and nine 

 shorter. The smallest specimen measured the -^th of an inch long, ^.th of 

 an inch broad, ^.th of an inch thick, with the oral end ^th of an inch by 

 gLth of an inch. The largest specimen was f J th of an inch long, ^th of an 

 inch broad, ~ t\\ of an inch thick, with the oral end 5 ^th by 8 J th of an inch. 

 The carina ranges from g^th of an inch to j4>th of an inch deep. 



The sarcode of Nebela carinata exhibits the same characters as that of 



