806 



DE. G. HERBEET FOWLEE ON THE 



[June 15, 



and while the Plymouth specimens acqiiire the characteristic 

 terminal pore at a stage of between 7 and 9 tentacles, it does not 

 become perforated in alhida 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 known adult Cerianthid 

 (?C. 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 larvse 

 by specific names is a reprehensible practice, still so much tow- 

 netting is no^^' 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. 



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

 (n. s.) L p. 321. 



Arachnactis bournei, sp. n. 

 Annually'. 



Described anatomically 

 by van Beneden, 

 Arch. Biol. xi. p. 115. 



,, „ „ Entrance to English July 1S89. 



Channel. 

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



Hist. (6) V. p. ,^06. corded only. 



Vallentin, Eep. E. Corn- Falmouth. Summer, 1890. (Not seen tbr some 



wall Tolyt. Soc. lix. years now.— E. Y.) 



Browne (unpublished). Port Erin, Isle of Jan. 1895. 



Man. 

 ., „ „ Valentia Island. March 1896. 



^ According to Garstang, March and April are the chief months for Arachnactis 

 at Plymouth. 



From A. albida, "v^liich 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 

 Sars' than by Vanhciffen'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, e.xcept 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 stomodaeum ; 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- 



