^°i89i!'''] PROCEEDINGS OF THE NATIONAL MUSEUM. 183 



rarity of specimens of this genus stands greatly in the way of a proper 

 knowledge of the range of their variations. The Arctic forms of this 

 group, e. g., Admete and Cancellaria modesta, vary greatly, but the 

 tropical forms are less known. As species go this appears to be suf- 

 ficiently distinct. It is named, at the request of Mr. Rivers, in honor 

 of Mr. A. W. Crawford, of San Francisco, a noted collector of shells, es- 

 pecially of that region. 1 may add that C. cassidiformis Sby. has been 

 collected near Cerros Island, off the coast of Lower California, as well 

 as G. obesa Hinds and G. bullata Sby. G. cassidiformis is also found 

 fossil in the Miocene or Pliocene formation of Santa Barbara County, 

 California. G. tritonidea Gabb and G. vetusta Gabb, from the Tertiary of 

 California, are based on a young and a very aged specimen, respec- 

 tively, of this variable species. 



Tellina Idae Dall. 



(Plate VI, Fig. 3. Plate vii, Figs. 1, 4.) 



Shell ovate-triangular, moderately elongate, white, compressed; ex- 

 terior of the right valve slightly flatter, and with more prominent sculp- 

 ture than the left valve ; beaks small, pointed, prominent, laterally com- 

 pressed, adjacent to each other 5 anterior jiart of the shell slightly longer 

 than the part posterior to the beaks, evenly and regularly oval, the 

 dorsal and basal curves almost identical ; posterior dorsal slope steeper, 

 rectilinear, obliquely truncate at its termination, the basal curve (behiud 

 the perpendicular from the beaks) similar to its anterior part as far as 

 the flexure, which is narrow but well marked, its basal end moderately 

 incurved; behind, it rises to a strong ridge the end of which forms a 

 rostral projection, behiud which, in the right valve, is a deeply impressed 

 line a little in advance of the posterior dorsal margin, which is strongly 

 compressed ; on the left valve there are two lines with a narrow impressed 

 area between them, above which the dorsal margin is swollen; in front 

 of the beaks is a narrow, acute, deeply excavated, short lunule; behind 

 the beaks is a large, narrow, still more excavated escutcheon, most of 

 which is excavated from the left valve, which falls short of the right 

 valve a little; the ligament is sunken in and about half as long as the 

 escutcheon ; it is quite invisible on a lateral view of the shell ; the left 

 valve is regularly, sharply, closely, concentrically grooved, and both are 

 obsoletel}^, finely, radiately striate; the margin between the impressed 

 area of the left valve and the escutcheon is more finely grooved than 

 the rest and has a (somewhat irregularly) denticulate dorsal edge ; the 

 right valve has the concentric sculpture more distant and, ventrally, 

 shows distinctly elevated narrow lines with wider interspaces regularly 

 disposed, and also bears denticulations on its posterior dorsal margin ; 

 the um bones are nearly smooth; the shell gapes but little, chiefly at the 

 end of the rostrum ; internally the surface of the valves is smooth, the 

 muscular and pall ial impressions are brilliantly polished; besides the 

 usual marks, in the specimen under examination there are, near the 



