806 



DR. G. HERBERT FOWLER O1ST 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 mm. in length 

 provided with 12 oral tentacles, or, according to Boveri, 17 marginal 

 tentacles. 



Until this Channel form be traced to a kno\vn adult Cerianthid 

 (?(7. lloydii, Gosse), I propose to distinguish it from A. albida by 

 associating with it the name of my friend Mr. G. C. Bourne, the 

 first Director of the Plymouth Station, under the style of Araclm- 

 actis bournei ; for although I admit that the christening of larva? 

 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.^ 



Arachnactis bournei, sp. n. 

 Annually \ 



Bourne, J. Mar. Biol. Assoc. Plymouth area, 

 (n. s.) i, p. 321. 



Described anatomically 

 t by van Beneden, 

 Entrance to English July 1889. Arch. Biol. xi. p. 115. 



Channel. 

 Mclntosh, Ann. Mag. Nat. St. Andrew's Bay. June 1890. Single specimen re- 



Hist. (6) v. p. 306. corded only. 



Vallentin, Eep. 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Browne (unpublished).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. 



Prom A. albida, which is slender and tapers markedly in late 

 stages, A. bournei 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 

 Bars' than by Vanhoffeu's figure), and the tentacles are often many 

 times the length of the body, in A. bournei oral disk and body have 

 about the same diameter, and the tentacles are very short. As 

 regards the colouring, my 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 mesenteries, in all 

 specimens of A. bournei 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 stomodseum ; in 

 A. albida they extend to ^ or g of this distance even in young speci- 

 mens, and in older ones some stretch for nearly the whole body- 



