288 PROCEEDINGS OF THE ACADEMY OF [1898. 



Isohnocbiton scabricostatus Cpr. var. 

 Ischnocbiton regularis Cpr. 



One specimen has but seven valves, but in all other respects is 

 perfectly normal. 



Iscb.nocb.iton Mertensii Midd. 

 Iscbnocbiton Cooperi Cpr. 



Iscbnocbiton (decipiens var. ?) sinudentatus Cpr. 

 Ischnocbiton (Stenoradsia) Magdalenensis Hinds. 

 Callistocbiton crassicostatus Pils. 

 Callistocbiton palmulatus var. mirabilis Pils. 

 Cbaetopleura gemmea Cpr. 

 Nuttallina Californica ' Nutt. ' Rve. 

 NuttallinaThomasi Pilsbry, n. sp. 



In tide pools with Tr. Raymondi. See below. 



MOPALIIDiE. 



Mopalia muscosa Grid. Typical. 

 Mopalia muscosa lignosa Gld. Typical. 

 Mopalia muscosa Hindsii 'Sow.' Rve. Typical. 

 Mopalia Heathii Pilsbry. See below. 

 Mopalia ciliata Sow. Typical. 

 Placipborella velata Cpr. 



ACANTHOCHITID.SI. 

 Katharina tunicata Wood. 

 Cryptochiton Stelleri Midd. 



One full grown specimen is 7-valved, otherwise normal. 

 Mopalia Heatbii n. sp. 



Oblong, rather elevated, carinated, with nearly straight side 

 slopes ; surface smoothish to the naked eye, lusterless, and in color 

 (1) olive-green with some lighter spots, or purplish maculation, or 

 slight roseate suffusion, or (2) vivid red, with scattered blue spots. 



Valves shaped as in M. lignosa, but without a median anterior 

 projection of the tegmentum; the intermediate valves very faintly 

 radially trisulcate at the sides, the anterior two grooves defining the 

 low, slight and inconspicuous diagonal rib, the lateral areas not 

 raised ; entire surface very finely and evenly granulate, the granules 

 small, rather pointed, separated, intervals very minutely, radially 

 wrinkle-granulate. Anterior valve with a few faint, shallow radial 

 furrows. Posterior valve with semicircular posterior outline, the 

 mucro in front of the middle of tegmentum, profile of the surface in 

 front of it convex, that of the posterior slope decidedly concave. 



