342 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. 57. 



Cat. No. 



110972 

 122545 



123141 



123142 



123143 



123140 



Locality. 



Catalina Island, California, 50 fathoms 



Off Cerros Island, Lower California, 113 

 fathoms 



Off Cerros Island, Lower California, 58 fath- 

 oms 



Northwest of Cerros Island, Lower California, 

 113 fathoms 



Off Point Abreojos, Lower California, 58 

 fathoms 



Off Point Abreojos, Lower California, 58 

 fathoms 



Collector. 



Lowe 

 B. F. 

 B. F. 

 B.F. 

 B. F. 

 B. F. 



Number 

 of speci- 

 mens. 



4 

 1 



13+ 



7+ 



20 



23 



The plus mark stands for many young specim.ens of various ages 

 in addition to the counted adults. Comparing the incongruity of 

 the types of plication with other characters of the species concerned, 

 it does not seem to me to have any serious systematic value in the 

 group of recent forms here under consideration. I am not able to 

 accept the compliment which Doctor Thomson has graciously con- 

 ferred upon me in proposing on that basis a new genus for the T. 

 dbsoleta. 



It differs from the other species of the coast in its thin and delicate 

 polished shell which contrasts strongly with the solid dull-surfaced 

 character of the others; its brilhant scarlet painting is equalled only 

 by such species as Laqueus pictus and Frenulina sanguinolenta. In 

 the completely adult there is on either side of the narrow deltidia a 

 flattened area with a keeled edge. Beecher's diagram (pi. 3, fig. 15) 

 of the loop is good but does not indicate the fact that the cardinal 

 plate is divided to the apex of the valve where there is a thin wide 

 cardinal process. A completely adult specimen measured 39 mm. 

 high, 42 mm. wide, and has a diameter of 21 mm. It exhibits the 

 wildest variations in plication from a barely preceptible protractive 

 arcuation of the anterior edge of the pedicel valve to a very strong 

 squarish ridge with four or five minor denticulations, to a ribbed form 

 with ten or twelve subequal modifications of the margin. There is 

 in the pedicel valve a very low slender septal median keel in the 

 hollow of the beak which terminates in a short broad low ridge with 

 an excavated top. There are small props to the hinge teeth from 

 which in senile specimens an arcuate raised line runs down into the 

 dome of the valve. In T. transversa the props are almost obsolete 

 and stop short behind the teeth; in the completely adult there is a 

 low flattish septal ridge extending beyond the middle of the pedicel 

 valve and forked at its anterior extremity. In fairly adult T. caurina 

 I find no trace of this ridge. In both there is a wdde thin cardinal 

 process and nothing resembling a cardinal plate between the dental 



