918 ERYCINID. 
Shell roundly subtrigonal, with somewhat produced obtuse 
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. 
Monrtacuta, Turton. 
Etym.—Dedicated to Colonel George Montagu, the most dis- 
tinguished of the earlier English malacologists. 
Syn.—Montaguia, Forbes. 
Distr.—12 sp. United States, Norway, Britain, Mazatlan. 
Aigean. M. substriata, 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. Lovén). 
Animal with the mantle open in front; margins simple; 
siphonal orifice single; foot large and broad, grooved. 
The Montacutz 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 oyster-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 Spatangus. 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 diagonally. 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 hundreds 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- 
