452 AXEL A. OLSSON 



equivalved and auriculate, and covers only a small portion of the anterior 

 end of the mollusk, the larger part of which is wormlike, often reaching a 

 length of several feet and it lies along a burrow, straight or tortuous, its 

 walls lined with a calcareous secretion forming a long, stout, winding tube. 

 The small valves, when separated from the animal, are in contact only along 

 the dorsal side and ventrally at the points of the parietal tubercle, elsewhere 

 the margins are apart or gaping; there are no accessory plates. Shell cavity 

 within the umbones has two slender apothyses, one in each valve. External 

 surface of the valves is divided into two sections by a median sulcus or 

 narrow furrow; the anterior section has strong sculpture formed by crenu- 

 lated or frilled concentrics, sometimes also with radials; the posterior sec- 

 tion with plain concentrics only. The distal ends of the siphons have their 

 openings guarded by two slender, feather-like structures known as pallets. 



The family is divided into two genera on characters of the pallets. 



1. Pallets of simple construction formed in one piece, the distal end 

 flattened, cup-shaped or paddle-like. 



Genus Teredo 



2. Pallets more complicated, segmented or plumose at the distal end 

 forming cup or cone-shaped vanes nestling one within the other. 



Genus Bankia 



The Teredos, or, as more commonly known as shipworms, are among 

 the most destructive of all marine, invertebrate animals causing heavy toll 

 of all kinds of wooden structures immersed in seawater such as wharfs, piling, 

 and in former days, of wooden-bottom ships. The many species are widely 

 distributed, occurring in all seas with the exception of the partially brackish 

 Baltic, but their identification belongs to the specialist, and requires collec- 

 tions containing the animal and shell, and especially the pallets; the latter, 

 club or feather-like structures composed of lime and chitin, and placed near 

 the siphons, and used to close-off the end of the tube. Several species have 

 been described from the Panamic region, some taken from the locks of the 

 Panama Canal; others from mangrove trees. Bankia dry as Dall was described 

 from specimens collected by R. E. Coker from living mangrove trees at 

 Tumbez, Peru. The majority of the species live in dead wood. 



Order ANOMALODESMACEA 



Superfamily ANATENACEA 



Family PANDOREDAE 



Shell with a crescentic or bladelike form, the valves unequal, the an- 

 terior side short, the posterior longer, often much elongated, its dorsal 

 margin straight or deeply concave, often terminating posteriorly in a sharp 

 point. The left valve is usually larger, strongly convex, the right valve 

 smaller, flattened, or deeply impressed. Inner surface of shell nacreous and 

 of a pearly white color, the outer layer thin and nondurable. The beaks are 

 erect but in the adult stage, generally corroded. The hinge is formed by 

 dentiform crural ridges or laminae, one or several in number, which radiate 

 from under the beak. Ligament internal, the tensilium being obsolete or 

 small, the resilium lodged in a deep groove below the posterior crural 

 lamina or between it and the more central crural lamina if one is developed. 

 Surface smooth or with radial markings. Ligament sometimes strengthened 

 by a calcareous plate known as the lithodesma. 



