DR. T. DAVIDSON ON RECENT BRACHIOPODA. 29 



Isle of Slioals, 20 fathoms ; Grand Manau, common (Packard, Stimpson) ; Halifax 

 harbom- (Willis); Trias Cove, Passamaquoddy Bay, in 12 fathoms, where they occm- 

 clinging; together in bunches, large and small together, and seem to prefer the clear 

 fresh water on pebbly bottoms (W. P. Ganong). 



Ohs. The above description is the one I published in my ' Challenger ' Report. Some 

 difference of opinion has prevailed with respect to the specific claims of the species under 

 description. Certain malacologists consider it a distinct species, others as only a simple 

 variety of T. capuf-serpeiitis. Gould, in 1838, believed it to be distinct ; but in the ' Report 

 on the Invertebrates of Massachusetts ' (2nd ed. by W. H. Binney, 1870) we find stated 

 at p. 208 : — " An examination of the descriptions of T. caput-serpentis given by Linnaeus, 

 Miiller, and Chemnitz, and a comparison of them with our shell, has well satisfied me of 

 their correspondence. The downy epidermis is a character too rare and singular to be over- 

 looked. This, however, is rubbed ofi" very easily. The shell is much thinner, in general 

 more elongated, and the strise nearly twice as nvimerovis, being about thirty to forty in 

 the Eui'opean, and fifty to sixty in the American specimens. No account of the internal 

 bony processes is given in any description except that of Mr. Couthouy. These would 

 afford the best possible specific character, were it not that they are usually more or less 

 broken. But I have been relieved from all further speculation by the receipt of specimens 

 from Dr. Loven, which settle the identity of om- species with the European caput-serpentis.'" 

 Mr. TV. H. Binney seems to be of a difi'erent opinion, for he adds, after Gould's observa- 

 tions just recorded : — " I have retained the above remarks from the former edition, because 

 our shell is so generally still regarded as identical with the European species. But further 

 examination of numerous specimens has led me to coincide with Dr. Stimpson, who has 

 dredged extensively, both in the British and American seas, in his opinion that the species 

 differs from the European caput-serpentis, sufficiently in both shell and animal." 



G. B. Sowerby, on p. 344 of his ' Thesaurus Conchyliorum ' (1846), observes that 

 T. septentrionalis is distinguished from T. caput-serpentis by its much finer radiating 

 striae, its larger and less oblique foramen, and by its rather more extended and somewhat 

 difi'erently formed internal appendage. 



Since publishing my description of this shell in the reports of the ' Challenger ' Expe- 

 dition, I feel more disposed to leave T. septentrionalis and T. caput-serpentis as separate 

 species, the first being evidently more regularly oval and rounded in front than in 

 Linne's species ; and even in the young stage the riblets are more numerous than in 

 T. caput-serpentis. I have been able to examine specimens from less than 1 line in 

 length up to that of 1 inch and 3 lines. Up to about 3 lines, and sometimes even more, 

 the ribs are very few in number, prominent and radiate from tlie extremity of the beak 

 to the margin, and are crossed by strongly indented concentric lines, which give to the 

 ril)lets the so-termed tuberculated appearance that has been so often described in the 

 species of this subgenus. As the shell grows the ribs become more delicate and more 

 numerous from repeated interpolations of shorter ribs, and tlie concentric ones become 

 more and more faintly marked. 



It is, however, to Prof. E. Morse that science is most indebted for the knowledge we 



