PELECYPODS 



429 



are not easily detected. They are not uncommon in such stations at 

 Mount Desert, Maine. 



M. plicatula. This species of Modiola ranges from Canada to Hat- 

 teras, and inhabits the tidal waters of streams, sheltered muddy reaches 

 among reeds, and tidal flats. It is a dingy-looking shell, ornamented with 



Modiola plicatula, typical f on 



numerous radiating ribs, which are very fine upon the anterior portion 

 of the shell. The epidermis is thin and of a dirty yellowish-green color. 

 Within it is silvery- white. In the ventral margin there is an opening for 

 the accommodation of a byssus. Length about three inches in New 

 England ; slightly larger at Norfolk. There is probably no muddy reach 

 of land that is exposed at low tide from Maine to the Carolinas that is not 

 inhabited by M. plicatula. 



M. tulipa. This is the " show shell " of the genus Modiola in American 

 waters. It belongs to the Southern fauna, and, like the others of its 

 genus, it moors itself to 

 wood or other solid ob- 

 jects by means of its 

 byssus. It is of about 

 the same size as the last 

 species, but is perfectly 

 smooth and of a bright- 

 yellowish color, with 

 dark rays over the cen- 

 tral portion. 



M. recta. A species 

 of Modiola fairly abun- 

 dant on the Pacific coast 

 from Vancouverto south- 

 ern California. It has a 

 long, narrow shell with a dark-brown glossy epidermis ; lighter pos- 

 teriorly, and with a short hairy growth. The interior is white. Length 

 three to four inches. 



ORDER PSEUDOLAMELLIBRANCHIATA 



This third order of Pelecypoda is made up of a number of fami- 

 lies m which the gills are filamentous, but in which the filaments 



