202 PALEONTOLOGY OF NEW JERSEY. 



very closely arranged, convex upward, and perforated hj an elliptical slit 

 of greater or less size. Six to eight of these dome-like septa are found in 

 the upper quarter of an inch of the tube, while the extremity is often con- 

 stricted longitudinally, so as to form a double opening. Below the lower 

 dome-like septum there is seen on the casts a double U-shaped or saddle- 

 shaped muscular impression, forming a continuous scar, but with two pro- 

 longations upward on the opposite sides and depressions between, the reced- 

 ing parts corresponding to the flattened side of the septal slit. 



Mr. Gabb first described the genus Polorthiis supposing it to be near 

 Vermetus, and i-emarks that "It has never been found burrowing, but grows in 

 aggregated masses of cylindrical tubes, almost always parallel and straight, 

 sometimes five inches long, slightly variable in diameter from irregular 

 constrictions, contains no shell, but the tube is divided at certain distances 

 by transverse septa, convex and thin, the convexity pointing toward the 

 widest (or newest) portion of the tube, as if the animal progressed along 

 the tubes, closing the spaces behind it, as in the manner of the Cephalopoda, 

 but hermetically." (Proc. A. N. Sci. Phil., 1861, p. 366.) In 1872, in the 

 same journal, p. 259, he again discussed the genus Polorthus, and refers it 

 to the Cephalopoda, under the impression that its relations were with that 

 group of mollusks, and considers it nearly related to Orthoceras, etc., from 

 the existence of the septa in the lower end of the tube and the absence of a 

 .shell like that of Teredo. It is hardly necessary to remark that the refer- 

 ence is very erroneous, and that its relations to the Cephalopoda is entirely 

 imaginary. The genus Kuphns, a forai of Teredo, does not possess shelly 

 valves, and Teredo Norvegica, Spengler, which Tryon quotes as a synon}-ni 

 under Teredo navimn Sellius, in his list of the TeredidcE, Am. Jour. Conch., 

 Vol. 3, possesses the septa at the upper part of the tube to a much greater 

 degree than does T. tibialis; neither do these forms always burrow in 

 wood, but frequently in sand, as these have done; still I have seen sev- 

 eral specimens of T. tibialis, which have burrowed into a black substance 

 resembling lignite, which may have been originally woody. One of these 

 is now in the possession of Mr. G. F. Kunz, of Hoboken, New Jersey. Con- 

 sidering all these circumstances, I see no reason for separating the present 

 ispecies from Teredo. 



