Two fleshy siphons at the tail end of the "borer, vhich peModt 

 It to talsB^ in and expel vater, may he extended as much as an inch 

 from the entrance to the tuimel; or the "borer may plug the tunnel at 

 vill "With a pair of calcareous tall memhers called pallets. Thus the 

 tunnel may "be sealed, ena"bling the "borer to withstand for seme time the 

 unf avora"ble conditions attendant upon removal to fresh water or into 

 thB open air. Thus the outside appearance of a piece of wood infested 

 "by marine "borers is often deceptive: a piece that appears to "be merely 

 dotted, with tiny entrance holes may in reality contain so many tunnels 

 that only a we"b of wood remains. 



"b. The Pholadidae . The Pholads are a family of "bivalve 

 "borers of which two genera, Martesia and Hiata, have "been frequently 

 found in wooden marine structures, Qilite different from the Teredinidae , 

 these small, flat, clam- 11 be "borers do not drill into wood much farther 

 than the length of their shell, which is usually not over two inches. 

 They make larger entrance holes than do the Teredinidae , however. As 

 they "burrow they, too, grow larger and imprison themselves in their own 

 tunnels. Although found around the entire world, Pholads are prevalent 

 in fewer num"bers than are Teredinidae and Limnoria and are conseq.uently 

 responsl'ble for much less damage, even though their attack is more 

 difficult to prevent. In this last connection, for example, it might 

 "be noted that wood heavily impregnated with creosote has frequently 

 "been f otmd "badly damaged "by Pholads although practically untouched "by 

 Teredinidae . 



5. The Crustacean Borers . The crustacean "borers, which are 

 almost always found in tunnels in vood, include Sphaeroma , Chelura , 

 and Limnoria . By far the most widely distrihuted and most destructive 

 of these is Limnoria , which are numerous in almost all har"bors, and 

 are found in arctic as well as tropical waters. 



a, Sphaeroma , also widely distrl'buted, is only occasionally 

 responsl'ble for the destruction of timher. 



"b. Chelura , until recently, has "been considered at least as 

 destructive In wood as Limnoria . Recent studies, however, seem to 

 indicate that this species has "been greatly overrated in its destructive 

 a"bilities, possl"bly "because Chelura are frequently discovered occupying 

 a"bandoned Limnoria txumels. 



c. Limnoria , most destructive of the crustacean "borers, are 

 only ahout l/8 inch long. Their "burrows are generally confined to the 

 surface of the wood, or to a depth which seldom exceeds jA inch. 



