152 MAZATLAN BIVALVES 
fry. It probably resembles P. costellata, Conr. from the 
Sandwich Is., but that is described as having both beaks alike. 
The smallest specimen is ‘05 in length; the largest, long. (the 
diagonal of the lozenge) 1°12, lat. °68, alt. °17. 
Hab.—Mazatlan; on I. Chemnitzii and Spondylus calcifer, 
extremely rare: L’pool Col. 
Tablet 689 contains 1 pair and 2 valves, very young.—690, 
the most characteristic specimen, in situ. 
Famity PECTINID 7: 
Genus PECTEN, Miil. 
Of this (in most places) abundant genus only 3 very small 
valves were found. The neighbouring genus Lima was alto- 
gether absent. 
207. PectEN crrcunaRis, Sow. 
Proc. Zool. Soc. 1835, p. 110.—Hanl. Deser. Cat. p. 271. 
Dull ash, variegated with chocolate ; ears very large ; inter- 
stices near the umbo finely decussated. The opposite valves 
differ in sculpture.— Long. °28, lat. °26, alt. *12. 
fab.—Guaymas ; in sandy mud, 7 fm.; Col. Cuming.—St. 
Vineent’s [?] Hanley.—Mazatlan; extremely rare: L’pool 
Coil. 
Tablet 691 contains the only valve I found. 
Famity SPONDYLID£. 
Genus SPONDYLUS, Linn. 
208. SPONDYLUS CALCIFER, 7. s. 
S.t. maxima, ponderosa, solidd, plerumque orbiculart ; rubro- 
purpureo ; valud superiore costis minimis aculeatis 
ereberrimis tecta, huc et illuc costis irregularibus squamosis + 
squamis curtis, ad basim arcuatis, supra foliatis ; valvd infer- 
zore plerumque foliata ; area ligamenti magna, ligamento haud 
tecto; intus subnacred, limbo lato toto purpureo, seu 
nonnumquam flavesco-rubente; margine extremo cre- 
berrime et minute crenulato; dentibus validis ; fossa 
ligamenti canalibus 2-6 parallelis, decussatis ; muse. tmp. sub- 
orbiculari, magna. 
