294 



The burrows of Baiikia characteristically penetrate piling more deeply before 

 turning to run parallel with the grain than do the burrows of Teredo in lightly infected 

 piling. In heavily infected timbers all burrows must of necessity go towards the center; 

 but in lightly infected piling the burrows of Teredo are usually more superficial than 

 those of Baiikia. 



Bankia, even more than Teredo, concentrates its attack near the mud line on 

 piling, so that its burrows, although fewer and more sparsely set than those of the 

 latter, are capable of speedily destroying the bearing power of untreated piles, even 

 though a few feet above the mud line the wood may be practically sound. 



Teredo diegensis 



This is an organism much smaller than Bankia, and smaller in general than 

 Teredo navalis, adults ranging in length from one or two to four or five inches. The 

 average size in San Francisco Bay is smaller than in harbors farther south. 



This species is at present of negligible importance in San Francisco Bay, and 

 its history during the four years it has been known to occur in this locality does not 

 indicate that it is likely to become a serious economic factor here. In Los Angeles and 

 San Diego harbors, however, quite the reverse is true. Teredo diegensis is in these 

 localities most numerous and destructive, constituting the real shipworm problem of 

 these ports. 



Teredo diegensis, like T. navalis, is viviparous, the offspring being retained in 

 the brood pouch of the female until a somewhat advanced stage of larval development 

 is reached. The larvae of diegensis are less numerous than those of navalis — 490 being 

 counted in the brood sac of a female two inches long — but are considerably larger, 

 so that the brood pouch of the female is greatly distended, the large, nearly globular, 

 brown-shelled larvae being plainly visible through the transparent body wall of the 

 parent (fig. 72). 



The lesser number of larvae carried in the brood pouch at one time, as compared 

 with T. navalis, is compensated for at least in part by the much longer breeding season. 

 The period of breeding activity in Los Angeles and San Diego harbors, in fact, includes 

 practically the entire year, although the settlement of larvae is much lighter during 

 the winter months. Test boards placed in San Diego Bay in December, 1922, indicated 

 some settlement of larvae of this species by January, although no heavy settlement 

 occurred until May. The growth of such larvae as found settlement during the winter 

 months was much retarded during January, February, and March, the maximum 

 length attained by March 16 being 3^16 inch. After the first of April growth increased 

 rapidly, a maximum length of three inches being attained by May 15. 



Test boards placed in Los Angeles Harbor afforded very similar data. Boards 

 placed in October, 1922, showed beginnings of attack by Teredo diegensis through 

 November, December, January and February. A maximum length of one inch was 

 reached b>- March 16. In April and May the settlement of larvae greatly increased, 

 and the rate of growth in the wood became accelerated. By September the 2" x 4" 

 blocks were entirely honeycombed by T. diegensis, of a maximiun length of about 

 5 inches. 



In general, then, it appears that in Los Angeles and San Diego harbors Teredo 

 diegensis breeds more or less continuously throughout the year, but that settlement of 

 lar\'ae is heaviest and growth most rapid during the period from April to October, 

 that is, during the warmer months of the year. Thus the temperature relations of this 

 species are quite the reverse of those of Bankia setacea. 



The occurrence and behavior of Teredo dies.ensis in San Francisco Bav has been 



