no SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 85 



fresh-water mollusks. The food of the wah-us consists mainly of 

 shellfish. Dyche reports that the California sea-lion feeds very largely 

 upon squids and octopods and it is known that squids form a con- 

 siderable proportion of the diet of sperm and other whales. 



The enemies of marine mollusks include also sea-anemones, star- 

 fishes, and boring univalves of the genera Purpura, Polynices, Thais, 

 Lunatia, Natica, Cycotypus, Fulgur, and Urosalpinx. Fresh-water 

 mollusks form an important element of the food of dragonfly nymphs, 

 and a lesser one of horse fly larvae, water beetle larvae, water bugs, 

 leeches, and crayfishes. Land snails are attacked by predacious 

 beetles and fly larvae. Alollusks also have enemies among such para- 

 sitic groups as mites, nematodes, and trematodes. 



Discussion. — From the abundance of their enemies and from the 

 extent to which these predators feed upon mollusks (more than 8,000 

 records for birds in our tabulations), it is evident that the possession 

 of a shell as a means of defense has been entirely discounted so far 

 as predators of any size are concerned. The relations of birds to the 

 protectively colored forms show that some of these (Litorinidae) are 

 freely eaten; the brightly colored shells (Pectenidae) also are freely 

 taken, as well as the very hard and thick-shelled ones (Ostreidae). 

 Slugs, snails, limpets, teredos, chitons, and cephalopods pay their toll 

 also, testimony to the all-pervading search for food by birds. In fact 

 the evidence is that birds feed more or less indiscriminately upon all 

 mollusks of suitable size that are available to them. Other enemies 

 follow mollusks, especially the marine forms, where most birds can 

 not, and it would seem that the whole molluskan world is exploited 

 as a source of food to as large an extent as could be expected. 



CHORDATA (lANCELETS, TUNICATES, VERTEBRATES) 



While the Chordata with 13.326 identifications contribute only 

 5.6133 per cent of the total determinations of the animal food of 

 birds, yet the phylum comprises so many familiar animals that it 

 probably will be best to treat it more in detail as was done in the case 

 of insects. 



Number of identifications, 13,326; percentage of identifications 

 among those of all animals, 5.6133; percentage of species in this 

 phylum among the whole number of animal species known, 8.8427. 



A tabulation of the records of Chordata with frequency indices de- 

 rived from estimates for the world fauna gives the following results : 



