MEGATEBENNUS. 183 



foot, and extends upward well over the margins of the shell. Its 

 edges, both above and below are smooth, thin. The epipodial ridge 

 is a simple raised line. The dorsal pore has no papillae or processes 

 around it. 



The specimen having been long in alcohol was much contracted 

 and of a uniform brown color. It is drawn on pi. 61, Fig. 11 repre- 

 senting a side view of animal with shell. 



Fig. 10 ventral aspect of foot, showing the head enveloped by the 

 mantle. 



Fig. 12 mantle cut away to show head with tentacle and eye, and 

 beginning of the epipodial ridge. 



Compare Dall's description of F. bimaeulata. 



M. BIMACULATA Ball. PI. 44, fig. 94. 



Shell ellipsoidal when young, subquadrangulate and a little nar- 

 rower in front than behind when adult. Aperture the same shape 

 as the shell, slightly encroached upon in some specimens tiy a point 

 on each side. External surface furnished with radiating rounded 

 costse, widening slightly toward the margin ; these are crossed by 

 evident but not very strong lines of growth, which in some individuals 

 are rather strong. Anterior declivity of the shell concave, sides 

 flattened, posterior declivity rounded convex. Color whitish with 

 numerous radiating rays of brown or slate color, usually with a 

 broad fasciculus of darker rays in the middle of each side extending 

 from the apex to the margin, and occasional dark dots on the ribs. 

 Shell occasionally entirely brown or slate-color, with two darker 

 rays on the sides. Epidermis none. Interior pure white, the two 

 dark rays sometimes showing through the shell. Extreme outer 

 edge finely denticulate or rounded and smooth according to the 

 stage of growth. Margin as a whole broad, smooth, differentiated 

 from the rest of the surface by a wide shallow groove. Margin of 

 the aperture similarly bordered. .Muscular .impressions distinct, 

 surface marked by fine radiating lines ; polished. Anterior and 

 posterior margins internally concave or emarginated, so that when 

 laid upon a flat surface in the natural position the ends of the shell 

 do not touch it. (Dall.) Length 16, breadth 10, alt. 31 mill. 



Monterey, Baulinas Bay, Santa Barbara, Purissima, and Lobitas, 

 Cal 



Fissurellidea bimacidata DALL, Amer. Journ Conch, vii, p. 132, t. 

 15, f. 7, 1872. Clypidella bimaculata DALL ms. 



