NATURAL SCIENCES OF PHILADELPHIA. 259 



NOTES ON THE GENUS POLORTHUS, Gabb. 

 BY WILLIAM M. GABB. 



In 1834, Dr. S. G. Morton, in Ms " Synopsis of the Organic 

 Remains of the Cretaceous Group of the United States," described 

 a species under the name of Teredo tibialis; mentioning a former 

 edition of the same work, when he says he " referred this species 

 to T.antenautse, Sby." (Min.Conch., vol. i. p. 231, pi. 102). Sow- 

 erby's shell is from the London clay, and Morton was correct in 

 separating the American species, which is Cretaceous. But while 

 correcting one error he fell into two others, not less grave. He 

 included all of the terediform tubes found in New Jersey under 

 the one name, and figured as the type of the species a shell which 

 1 believe is not only not a Teredo, but is Cephalopod. There 

 are at least two species mentioned by Morton (Srjn. Cret., p. 69) ; 

 and for the one figured and described, the specific name must be 

 retained. For the other I proposed the name of T. irregularis. 

 in 1860 {Jour. Philad. Acad., 2d ser. vol. iv. p. 393, pi. 68, fig. 19). 



In 1861, while examining Dr. Morton's specimens, I was struck 

 by some peculiarities in the tubes, which, on further study, in- 

 duced me to propose the above generic name, and suggest the 

 relationship of the genus to Vermetus. Since then the matter 

 seems to have been forgotten, until recently my friend, Dr. 

 Stoliczka, in his able work on the Fossils of India (Pal. Indica, 

 vol. iii. p. 14), quotes the name doubtfully and at second hand for 

 the Smithsonian Check List, and in the Pholadidse. This last 

 fact has determined me to call attention to the genus in a more 

 explicit manner than the original imperfect notice, in the Pro- 

 ceedings of the Academy, 1861, p. 366. 



P. tibialis, Morton, is the species for which the name was first 

 proposed. At the time I described the genus, I was in receipt of 

 a fine series of specimens of my Gastrochsena Americana, from 

 the " Ripley Group" of Tennessee, sent me by Prof. Safford, the 

 State Geologist, and I found that the two forms were congeneric, 

 although I have never yet seen the apex of the latter species. 



The generic characters are as follows : Shell tubular, growing 

 singly or in clusters, nearly straight. Interior divided into cham- 

 bers by two entirely different sets of septa. In the young state, 



