218: ERYCINID^. 



Shell roundly suMrigonal, with somewhat produced ohtuse 

 beaks, nearly equilateral ; surface only concentrically striated ; 

 hinge with an anterior (sublunular) elongated cardinal tooth in 

 each valve, in the right separated from the margin by a deep 

 groove ; cartilage in a pit situated below and a little posterior 

 to the beaks ; muscular impressions rather large, equal. 



MoNTAcuTA, Turton. 



Etym Dedicated to Colonel George Montagu, the most dis- 

 tinguished of the earlier English malacologists. 



8yn. — Montaguia, Forbes. 



Distr. — 12 sp. . United States, IJ'orway, Britain, Mazatlan. 

 jEgean. Jf.swfes^ria^a, Forbes (cxx, 85). Fossil, 2 sp. Pliocene — ; 

 Britain. 



Shell minute, thin, oblong, anterior side longest ; hinge-line 

 notched ; ligament internal, between two laminar, diverging 

 teeth (with a minute ossicle. Loven). 



Animal with the mantle open in front ; margins simple ; 

 siphonal orifice single ; foot large and broad, grooved. 



The Montacutse moor themselves by a byssus, or walk freely ; 

 M. substriata has only been found attached to the spines of the 

 purple heart urchin ( Spatangus purpureus) in 5-90 fathoms. 

 M. bidentata burrows in the valves of dead oj^ster-shells. 



The byssal threads by which this curious mollusk attaches 

 itself are exceedingly coarse and strong. Mr. Clark observed 

 it in active motion after he had separated it, still adhering to 

 the spines, from a Spatangvs. He says : " When the animal 

 marches, its foot is extended, and its rounded termination is 

 instantly fixed to the vase in which it is deposited ; then by the 

 retractor muscle it is drawn forward, making such rapid pro- 

 gression as to cross a watch-glass in a minute, and on the passage 

 turns itself several times by a twist of the foot from side to 

 side. 



" The gills and green liver are visible through the shell in some 

 specimens which are more transparent than others, the former 

 crossing it diagonallj^ The shape and position of the cartilage 

 is very remarkable. Sometimes the shell is partly incrusted 

 with a ferruginous deposit. The number of fry, with their shells 

 completely formed, which are found in some individuals, is 

 astonishing. Many hundi'eds of them, packed close together, 

 and glittering like microscopic pearls, might be counted. They 

 occupy at least two-thirds of the space enclosed within the 

 valves of their parent ; and its own body seems to be atrophied 

 and dwindled to a mere skeleton. The shell is in fact turned 

 into a crowded nursery. Perhaps the parent dies, like some 

 insects, immediately after all its progeny have been developed. 

 I do not concur in the general belief that M. substriata is para- 



