188 



SCIENCE. 



[N. S. Vol. IV. No. 85. 



to take such an exhaustive survey of 

 biological data as Darwin did in his 

 time. The enormous mass of accumu- 

 lated facts already far transcends the 

 power of any one mind to grasp, and it 

 would seem that organized cooperation is 

 the only method of dealing with such vast 

 accumulations. When that time arrives, 

 the paleontologist will be able to render 

 even more conspicuously valuable services 

 that he has done in the past. 



W. B. Scott. 

 Pkinceton University.. 



ON PHOLADIDEA PENITA AND ITS METHOD 

 OF BOEING. 



The Piddock of the northwestern coast, 

 Pholadidea penita, is found in its curved 

 conical burrow in the rocks near the tide 

 marks. These rocks, so far as the writer's 

 observation goes, consist of soft limestone 

 or sandstone of varying hardness, the 

 animal choosing the softer portions for its 

 home. How the Piddock accomplishes the 

 task of burrowing into the even moderately 

 hard sandstone is a question upon which 

 little light is thrown by an examination of 

 the mature, or as I shall call it, the resting 

 form, which is characterized by the com- 

 plete absence of its foot muscles and an al- 

 most complete fusion of the mantle lobes 

 along their ventral margin, leaving an 

 opening hardly 2 mm. long. The inference 

 is that Pholadidea penita is a degenerate 

 form, as is the oyster. Further facts, how- 

 ever, will show that this degeneracy does 

 not occur till late in life, when its burrow, 

 the home of its old age, is completed. 



The shell of the animal during its period of 

 diligence, like that of other Piddocks, gapes 

 widely in front. Through the upper por- 

 tion of this gape protrudes a thick fold of 

 the mantle which overlaps the antero-dor- 

 sal margin of each valve and secretes a 

 layer of calcareous matter on the outside of 

 the shell. The gape is much wider below 



Fig. I. Left side of resting form, specimeii 9 cm. 

 long. 



Fig. II. Left side of working form, specimen 6 cm. 

 long. 



Fig. III. Inside of left valve shovping hinge mechan- 

 ism and muscle markings, specimen 9 cm. long ; 

 Siphon retracted in all. aa. Anterior adductor 

 muscle mark ; the arrov7 point indicates its 

 posterior limit. 3a. Third adductor muscle mark 

 at angle of pallial sinus, f. Cuticular flap. ft. 



" Foot. m. Thick antero-ventral edge of mantle 

 surrounding foot. p. Pad formed by antero-dorsal 

 mantle folds, pa. Posterior adductor muscle mark, 

 pi. 1. Plate secreted by antero-dorsal mantle fold, 

 of that side. pi. 2. Plate secreted by m. in Fig. II. 

 S. Additional extent of shell added at the same 

 time with cuticular flap. u. Umbo. The leaders 

 end in patch of abrasion, the point where the valves 

 articulate. The small crosses indicate attachment 

 of hinge cuticle. 



and through it protrudes a strong cylindri- 

 cal muscular foot, the muscles of which are 

 attached at a point of vantage supplied by 

 a curved process on the inside of each 

 valve. The mechanical result of this ar- 



