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Show 806 DR. G. HERBERT FOWLER ON THE [June 15, and while the Plymouth specimens acquire the characteristic terminal pore at a stage of between 7 and 9 tentacles, it does not become perforated in albida until a stage of about 8 m m . in length provided with 12 oral tentacles, or, according to Boveri, 17 marginal tentacles. Until this Channel form be traced to a known adult Cerianthid (?C. lloydll, Gosse), I propose to distinguish it from A. albida by associating with it the name of m y friend Mr. G. C. Bourne, the first Director of the Plymouth Station, under the style of Arachnactis hournei; for although I admit that the christening of lame by specific names is a reprehensible practice, still so much tow-netting is now carried out every summer all round our coasts that it is advantageous that well-marked species of even larval forms should have a name under which their occurrences may be chronicled. Bourne, J. Mar. Biol. Assoc. Plymouth area. (n. s.) i. p. 321. Arachnactis bournel, sp. n. Annually1. Described anatomically by van Beneden, „ „ „ Entrance to English July 1889. Arch. Biol. xi. p. 115. Channel. Mcintosh, Ann. Mag. Nat. St. Andrew's Bay. June 1890. Single specimen re- Hist. (6) v. p. 306. corded only. Vallentin, Rep. R. Corn- Falmouth. Summer, 1890. (Not seen for some wall Polyt. Soc. lix. years now.-R. V.) Browne (unpublished). Port Erin, Isle of Jan. 1895. Man. „ „ „ Valentia Island. March 1896. 1 According to Garstang, March and April are the chief months for Arachnactis at Plymouth. From A. albida, which is slender and tapers markedly in late stages, A. hournei is recognizable by its fat cylindrical body and sharply rounded end; further, whereas in A. albida the union of the swollen bases of the tentacles produces an " oral disk " much greater in diameter than the body (a point better brought out by Sars' than by Vanhoffen's figure), and the tentacles are often many times the length of the body, in A. bournel oral disk and body have about the same diameter, and tbe tentacles are very short. As regards the colouring, m y friend Mr. E. T. Browne informs me that he has taken this form on several occasions, and that in colour it is yellowish or brownish all over : it thus presents a great contrast to A. albida, which is of a transparent bluish-white, except for the yellowish-brown tips of the tentacles; in older specimens of albida the body may also assume a brown tint, but the tentacles remain transparent even in my oldest stages. The meseuteries, in all specimens of A. bournel which I have been able to examine, have an extremely short course, extending only about J to 5 of the length of the body below the free end of the stomodaeum ; in A. albida they extend to \ or \ of this distance even in young specimens, and in older ones some stretch for nearly the whole body- |
