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Show •106 DR. GWYN JEFFREYS ON MOLLUSCA OF THE [Apr. 16, and other seas. The septum in the very young of T. cranium consists of a mere upright point, as in Megerlia ; and the loop is then round and small, becoming elliptical and extended in the adult. The foramen is incomplete in the young of T. septata, and resembles that of T. cranium in every state ; and this is likewise the case as to the young of T. vitrea. Mr. Dall, in the 'American Naturalist' for March 1871 (vol. v. p. 55), indicated a new genus of Brachiopods, founded on some young specimens of T. cranium which I had sent him from the 'Porcupine' dredgings in 1869. He said the loop " has no secondary attachment to the haemal valve, and the latter is destitute of a septum." This genus he proposed to name Frenula, and the species Jeffreysii. In the American Journal of Conchology for 1871 (vol. vii. pt. 2, p. 65, pl. ii. figs. 7-10) he gave a more detailed account, with figures, of the same species as Ismenial jeffreysi. His figures agree with those published by Herr Friele to illustrate the development of the skeleton in T. cranium. Mr. Dall remarks as to his species, " Without a septum in either valve. Loop unattached except by the haemal processes to the hinge plate," and further on, " None of the specimens had the slightest trace of a septum." He then alludes to having subsequently received from me other young Brachiopods, of which he says, " All of them possessed a filiform but rather stout septum ;" and, although with some doubt, he was of opinion that all the specimens belonged to the same species, and that in those first mentioned "the septum must have been broken away." He has since, at m y request, kindly sent me for my inspection a specimen of his species, which he now calls Megerlia jeffreysi, and which he says he received from me as the young of T. cranium; and he has presented me with some valves dredged by him at Port Etches in Alaska, at a depth of about 15 fathoms, and which according to him were " probably " the same species, although he carefully explained that he would not vouch for it. The valves in question were worn and apparently old, but all of them showed the septum most distinctly; and they may belong to the species which Mr. Dall has very lately described anew as Megerlia jeffreysi. These valves are not unlike Terebratella (?) frontalis of Middendorff in shape and texture; but they differ essentially in the position of the septum as well as in the deltidium. In Mr. Dall's imperfect specimens the septum resembles that of Terebratella spitzbergensis, viz. in being a long narrow and threadlike lamina extending from the middle of the deltidium for about two thirds of the inside towards the front; in T. frontalis (judging from the type most obligingly sent me by Dr. v. Schrenck from the St. Petersburg Museum for my inspection) the septum is that of Argiope, being gnomon-shaped or triangular, and placed near the front. The apophysis of Megerlia truncata does not correspond with that of any of the above-named species. I would here remark that the septum is not at all likely to be broken away and entirely disappear, because it is formed in the protected part of the lower valve. It is persistent in the most worn and even fragmentary spe- |