MARYLAND GEOLOGICAL SURVEY 729 



but the valves are smaller and so much more compressed that it seems 

 hardly probable that the limits of variation even in Martesia are wide 

 enough to include both forms. 



Occurrence. MATAWAN FORMATION. ? Marl pit near Post 236, 

 Chesapeake and Delaware Canal, Delaware. MONMOUTH FORMATION. 

 ? Brightseat, Prince George's County, Maryland. 



Collections. Maryland Geological Survey, Philadelphia Academy of 

 Natural Sciences, New Jersey Geological Survey. 



Outside Distribution. Matawan Formation. Merchantville clay marl, 

 Marshalltown clay marl, New Jersey. 



Family TEREDINIDAE 



Genus TEREDO Linne 

 [Systema Naturae, ed. x, 1758, p. 651] 



Type. Teredo navalis Linne. 



Shell much reduced ; valves trilobed, widely gaping anteriorly and pos- 

 teriorly; surface concentrically striated; hinge margin reflected, edentu- 

 lous; spoon-shaped process projecting from interior of hinge for attach- 

 ment of pedal muscle; anterior adductor degenerate; pallial line 

 coincident with the margins of the valves. 



The recent representatives of the species, the so-called ship-worms, have 

 been notorious since the days of the Roman Empire. To-day they occur in 

 the temperate and tropical seas in numbers sufficient to endanger all sub- 

 marine wooden constructions, whether ships, wharves, piers, bridges, piles 

 or dikes. Protection is gained only by metal sheathing or by treatment 

 Avith creosote. 



The genus has a long pedigree. Certain burrows from the Carbonifer- 

 ous have been referred doubtfully to the Teredo, and there is no question 

 that it existed in the Mesozoic. 



A. Posterior extremity of shell lobate dorsally; tubes circular in cross- 



section Teredo irregularis 



B. Posterior extremity of shell slightly produced dorsally but not lobate; 



tubes lenticular in cross-section Teredo rhombica 



Etymology: Teredo, a name given by Pliny to a worm that gnaws wood. 



