CLASS GASTROPODA 
45 
Seven species of Micranellum are known living in northwestern 
America. Five of these have the plug at the trunkated apex, forming an 
attenuated, obliquely placed spur, the base of which is narrower than the 
diameter of the plug. Of these, Micranellum pedroense, catalinense, and 
profundicolum have the anterior portion of the adult shell bulbously ex¬ 
panded, while in the other two, M. barkleyense and oregonense, the diameter 
does not increase at the anterior termination. Of those with the bulbously 
expanded anterior portion, M. pedroense has very fine, closely spaced annu- 
lations, there being about a hundred present in the adult segment of the 
shell, while in M. catalinense and profundicolum the annuli are less nu¬ 
merous and more pronounced, there being about seventy-five in the last 
segment. The shell of M. catalinense is shorter and stouter than of M. 
profundicolum. The two species which lack the bulbous anterior expansion, 
M. barkleyense and M. oregonense, are distinguished from each other at 
once by their great difference in size, M. barkleyense being both longer 
and thicker than Micranellum oregonense. Two of the seven species, M. 
rosarium and M. cerbricinctum, have the spur of the plug expanded basally 
to cover the entire width of the plug. Of these, M. rosanum is easily dis¬ 
tinguished from M. cerbricinctum by being much longer and having the 
annuli much more distinct than M. cerbricinctum. (Bartsch.) 
Range. Western North America. 
Type. Caecum crebricinctum Carpenter. 
Distribution. Alaska to San Diego, California. 
Micranellum crebricinctum Carpenter, 1864 
Proceedings of the California Academy of Sciences, 3:215. Tryon, Manual of 
Conchology, 8: PI. 67, figs. 71, 83. 
C (Anellum) t., quoad genus, magna tereti, solidiore, rufofusca, inter- 
dum radiis intensioribus longitudinalibus ornata; annulis gracillimis, cre- 
berrimis, rotundatis, haud elevatis circ. lxxx. cincta; interstitiis nullis; 
sculptura longitudinali nulla; apertura acuta, vix contracta, vix declivi; 
septo subangulato, submucronto; margine laterali recto; apice acuto, ad 
angulum circ. 45° maxime elevato; operculo vix concavo, lira spirali ele- 
vata. Long., 0.14; lat., 0.04 poll. (Carpenter.) 
This is a shallow water species abundantly distributed from Monterey 
to Lower California. (Bartsch.) Large, with aspect of Elephantulum, 
but very fine close annular sculpture; plug subungulate. 
Described as Caecum. 
Type in State Collection, No. 388. Type locality, San Diego, California. 
Range. Monterey, California, to Todos Santos Bay, Lower California. 
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