THE NAUTILUS. 105 



over the margin ; interior pearly, of a livid color. Length four and 

 a half inches ; height two and a quarter; breadth two inches. 



It inhabits the ocean in deep water, attached to the larger seaweeds, 

 and is thrown up on ocean shores in storms, the seaweeds being torn 

 from the rocks by tlie action of the waves and dashed upon the beach. 

 Sometimes these shells attain a length of six inches and are subject 

 to oreat variety of form, being almost always distorted in some man- 

 ner. In young specimens, the epidermis at the lines of growth is 

 prolonged into tilaments. 

 205. Modiolus plicatidus Lam. 



Shell transversely oblong-ovate, elongated, narrowed at the an- 

 terior and broadened at the posterior; beaks at the anterior end; 

 hing^ margin straight, ascending for two-thirds the length of the 

 shell, then curving downward and rounding at the posterior to meet 

 the basal margin ; surface ornamented with numerous radiating, 

 sometimes undulating, prominent ribs ; a broad elevated ridge runs 

 from the beaks to the posterior end of the basal margin, dividing the 

 shell into two nearly equal parts ; on the upper half of the shell thus 

 divided, the ribs are large and coarse, but on the lower half they are 

 very fine, merely lines on a smooth surface ; exterior silvery white, 

 covered by a thin varnish epidermis of a brown color, rayed with 

 zones of yellow, green and black ; interior silver white ; margins 

 crenulated. Length three inches, height one and a quarter, breadth 

 nine-tenths. 



This species, with the exception of Mya arenaria and perhaps 

 llyanassa obsolela, is the most abundant mollusk in R. I. It inhabits 

 everywhere in mud, peat bogs, salt marshes and in the banks of 

 rivers. It is found up the Blackstone nearly to Pawtucket, where 

 the fresh water is continually pouring over the falls, as well on the 

 shores of the bay and ocean. Its station is everywhere above low 

 water, and they cluster so thickly together as to frequently form 

 banks a foot or two in depth imbedded near high water, forming 

 beds sometimes hundreds of feet in length by ten to twenty in width. 

 When found completely buried in mud, they are generally preserved 

 in good condition, but if taken under any other circumstances, the 

 epidermis is found to be badly eroded, not only at the umboes, where 

 shells usually exhibit this peculiarity if at all, but all over the sur- 

 face. They may be gathered in any quantity in Providence, in the 

 banks of the river road, above Red Bridge. 



