90 MAZATLAN BIVALVES 
a Gastrochena truncata in its burrow, and a Petricola robusta 
which, after penetrating to the ?rock, has flattened itself 
rather than bore into the harder substance. 
122. CHama spinosa, Brod. 
Proc. Zool. Soc. 1834, p. 150.—Rve. Conch. Icon. in loc. 
Three small valves and one pair appear to belong to this 
species. The valves differ from the young of C. frond. fornicata, 
in having the entire surface crowded with semi-tubular spines ; 
and in the character of the margin, which is smooth and 
rounded within, outside with crowded scales one on another, 
like the base of Hipponyx tessellata. The types and the pair 
do not display this structure, which appears very characteristic. 
Hinge teeth comparatively small; muscular scars not very 
large ; colour white, with slight rosy tint at the umbos which 
are scarcely spiral. Long.1°1, lat.1°1, alé. °08. 
Hab.—Lord Hood’s Island, Cuming.—? Mazatlan; extremely 
rare; L’pool Col. 
Tablet 444 contains avalve. The pair will be seen, attached 
to Ostrea, with Discina, on tablet 20. 
123. Coama PExoGcyrRa, Conr. 
One broken pair attached to a pebble, and a valve on Spondy- 
lus ealeifer in the Liverpool Museum, differ from the rest of 
the Mazatlan Chame in the following particulars. Shell sinis- 
tral; ventrally produced; surface roughened and laminated, 
not spinous; margin smooth, rounded off, slightly crenate 
outside; teeth long, small, colour reddish brown, without 
purple. They may belong to Ch. Panamensis, or even to Ch. 
corrugata, but seem best to accord with this species. Long. 1°5, 
lat. V7, alt: 1°15. 
Hab.—Sta. Barbara, San Diego, &c. Nuttall—Mazatlan ; ex- 
tremely rare ; L’pool Col. \ 
Tablet 445 contains the specimen on pebble. 
Famity CARDIAD. 
Genus CARDIUM, Lunn. 
Only two species of this abundant genus were sent in any 
quantity ; the shell washings however proved that many more 
must exist in the neighbourhood ; 5 species being found suf- 
