598 MOLLUSCA 



P. truncata Say (Fig. 943). Shell 73 mm. long, 37 mm. high, and 

 31 mm. wide; elongate; anterior end triangular and sharply pointed, 

 posterior end broad and truncated; anterior portion with radiating 

 ridges; accessory valves calcareous: Massachusetts Bay to west coast of 

 Florida; common in the southern states. 



2. ZIRPHJEA Leach. Shell oval; cardinal margin slightly reflected; 

 no accessory valves ; umbo protected by a membrane : 3 species. 



Z. crispata (L.) (Fig. 944). Shell thick, 

 white, rounded posteriorly, triangular and 

 pointed anteriorly, gaping widely at both 

 ends; surface divided into equal halves by a 

 broad furrow extending from the umbo to the 

 Fig. 944 Zirphoea crispata lower margin, the anterior half marked by 

 numerous coarse ridges ; length 60 mm. ; height 



35 mm. ; width 34 mm. : circumpolar, south to Cape Hatteras and Cali- 

 fornia, boring in clay and wood in 9 to 70 fathoms, common towards the 

 north; Europe. 



FAMILY 2. TEREDIDAE. 



Ship worms. Animal vermiform, with very long siphons which are 

 united the greater part of their length and have 2 calcareous pieces called 

 the pallets (Fig. 945,2) at the point where they separate; valves 3-lobed, 

 very small, gaping at both ends, forming thus a ring with an interior 

 curved muscle process extending from the umbonal cavity: 2 genera; 

 7 species on the Atlantic coast; the animals live in long burrows in wood 

 or clay, which they form probably by the rasping motion of the shells 

 and then line with a calcareous coating; they often do great damage to 

 ships and docks; the burrows usually follow the grain of the wood, but 

 not always, and usually do not run into one another. 

 Key to the genera of Teredidae: 



a t Pallets spatulate 1. TEREDO 



o a Pallets feather-shaped 2. XYLOTRYA 



1. TEREDO L. Body globular, lying at the inner end of the burrow; 

 valves 3-lobed, the center lobe being the largest; mantle lobes united, 

 with a minute opening for the foot; siphons united nearly to the end: 

 about 20 species, 6 on the Atlantic coast. 



Key to the species of Teredo here described : 

 o x Tubes about C mm. in diameter. 

 &! Stalk and blade of pallet of equal length. 



c t Posterior lobes of shell much larger than the anterior T. NAVALIS 



c 2 Posterior and anterior lobes of equal size T. NORVEGICA 



b a Blade of pallet much longer than the stalk. 



G! Blade of pallet obovate T. MEGOTARA 



c a Blade of pallet oval T. THOMPSON! 



o a Tubes about 3 mm. in diameter T. CHLOROTICA 



