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and their habits are now pretty well understood. The modifications of the 

 animal, and of its shell-secreting functions, serve for their distribution into 

 four genera — 



Teredo. Gastroch^ena. Clavagella. Aspergillum. 



Genus 1. TEREDO, Adanson. 



Animal; vermiform; mantle tubular, slightly open anteriorly; 

 sip/ions very long, bifurcating at their extremities ; orifices 

 fringed, a muscular ring into which are inserted two variously- 

 shaped ossicles or pallets at the part where the siphons divide ; 

 branchiae continued into the siphonal tube; foot rudimentary, 

 sucker-shaped. fForbes.J 



Shell ; globose or hoop-like, equivalve, very largely gaping ante- 

 riorly, with a slender elongated apophysis springing from within 

 the umbo, or what is homologous loith the umbo, of each valve ; 

 hinge ligament obsolete, no accessory plates. 



It is chiefly to the destructive habits of the Teredo that we are indebted 

 for the care with which its history has been investigated. Though de- 

 scribed as a worm by Theophrastus, Pliny, Ovid, and succeeding writers, 

 including even Linnaeus, more than a century has elapsed since it was 

 made known by Sellius to be a mollusk ; and its ravages in the wood of 

 ships and harbours have been the theme from time to time of numerous 

 memoirs, including the reports of at least three official government com- 

 missions.* The Teredo may be likened to a Pholas, of the Xylophaga form, 

 whose habit is to enclose itself within a tube, sometimes club-shaped, 

 free or agglutinated in numbers together, but mostly tunneling into wood 

 to the length of from a few inches to between two and three feet. The 

 siphons, together with the mantle, are elongated through the posterior 

 gape of the shell to these various lengths according to the species, the tube 

 being secreted as the creature advances in boring, and the siphons of which 

 the bifurcated extremity remains at the posterior or narrow end of the tube 

 are strengthened by a muscular collar, out of which spring a pair of shelly 



* " In 1733 Holland was seriously threatened by the boring of our little shell-fish, and Dutch- 

 men by that of his biographers. Strange to say, its history, ' civil and natural,' was worked 

 out, not by zoologists, but by political writers, and with much care did they execute their task. 

 The investigators were Pierre Massuet, Jean llousset, aud Godfrey Sellius. They worked inde- 

 pendently of each other. . . . Sellius was a native of Dantzic. His work on the Teredo, a 

 small quarto of 360 pages, is a most remarkable production. In it all the learning of the 

 ancients aud of the moderns up to his time is brought to bear upon the history of the shipworm, 

 or to ornament by apt quotations the digressions suggested by his subject. Nearly two hundred 

 authors are cited. More than once, among the many scraps of ancient poetry with which he 



