. The sea-beach at ebb-tide : a guide to the study of the seaweeds and the lower animal life found between tidemarks . slandicus and P. irradians or dislo-catus. The first is P. hastatus of Puget Sound. Valves of this exquisiteshell are even occasionally found in California. It has very much the aspect of P. islandicus -unequal ears and an ovateform. The most curiousthing about this shell is thefact that a different systemof sculpturing exists uponthe two valves. Upon onethe ribs are even and thewhole surface is coveredwith raised scales; uponthe other the ribs are alter-nately of large and sm
. The sea-beach at ebb-tide : a guide to the study of the seaweeds and the lower animal life found between tidemarks . slandicus and P. irradians or dislo-catus. The first is P. hastatus of Puget Sound. Valves of this exquisiteshell are even occasionally found in California. It has very much the aspect of P. islandicus -unequal ears and an ovateform. The most curiousthing about this shell is thefact that a different systemof sculpturing exists uponthe two valves. Upon onethe ribs are even and thewhole surface is coveredwith raised scales; uponthe other the ribs are alter-nately of large and smallsize. Color rose-pink, withdeeper bands; one valvelighter-colored, suffusedwith delicate pink. Heighttwo and a half inches.(Plate LXXIX.) P. cequisulcatus. TheSouthern species above re-ferred to as resembling or dislocatus. Ithas about twenty stout,well-rounded ribs, with concentric wrinkles between them. The earsare equal. The size and shape are as in P. irradians. The coloring iswhitish, varying to shades of brown, and excentrically marked withspots or waving transverse lines of chestnut or Pecten irradians, typical form. ORDER EULAMELLIBRANCHIATA With the pectens we leave behind all pelecypods with thetrue filamentous type of gill. In the order EnlamelUltranclu-ata we find all the families to be possessed of the basket-work or crisscross branchial structure. Each gill is fun-damentally formed of filaments which project downward, andthen suddenly turn upon themselves and ascend; the ascendingand descending limbs are connected, however, by processes ofpresumably vascular function, and adjacent filaments are con-nected by truly vascular channels. The closer connection of thefilaments to form of each gill a sort of plate is further effected PELECYPODS 439 by connective tissue, which sometimes is dense enough (thoughalways porous) to obscure the reticulated appearance of theorgan. Furthermore, the edge of the outer lamella of the outergill unites with the ma
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectmarinea, bookyear1901
