m 



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 



rid^-es; accessoiy valves calcareous: Massachusetts Bay to west coast of 



Florida; common in the southern states. 



2. ZiRPH^SA Leach. Shell oval; cardinal margin slightly reflected; 



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



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



vi^iJm 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 

 (Gould). 



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. TEEEDIDAE. 



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: 



Oj Pallets spatulate 1 . Teredo 



o. 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 : 

 Oi Tubes about 6 mm. in diameter. 

 6i Stalk and blade of pallet of equal length. 



Ci Posterior lobes of shell much larger than the anterior T. navalts 



Cj Posterior and anterior lobes of. equal size T. norvegica 



bj Blade of pallet much longer than the stalk. 



Ci Blade of pallet obovate T. megotara 



Cj Blade of pallet oval T. thompsoni 



a. Tubes about 3 mm. in diameter T. chlorotica 



