Occurrence of Halistemraa in British Waters. 413 



beautiful specimens of Crinoids and Cystidea have been 

 collected." 



Now deep-water forms are, at the present day, usually more 

 ancestral than contemporary shallow-water forms, and the 

 same rule seems to have held good in past ages ; we may 

 therefore reasonably suppose that, while B. pinnulatus was 

 living in shallow water at Dudley, other more ancestral forms 

 were living in deeper seas, and that, as the Dudley sea-bottom 

 sank, these latter forms came in. Even if this be not allowed, 

 it must be remembered that the rarity of well-preserved 

 Crinoids in all beds below the Upper Wenlock Limestone 

 renders any objections based on negative evidence of very 

 small moment. 



XLII. — On the Occurrence of Halistemma in British Waters. 

 By the Rev. A. D. Sloan, M.A., B.Sc. (Edinb.), St. 

 Andrews. 



[Plate XII.] 



The first Siphonophore recoi-ded in St. Andrews Bay was 

 obtained in the bottom tow-net some distance off the Castle on 

 the 16th of May. When brought into the Marine Laboratory 

 it was in a moribund condition, and was preserved in alcohol 

 before it was given me for examination. Unfortunately the 

 bracts had all fallen off and the tentacles were very much 

 contracted. 



The specimen evidently belongs to the genus Agalmopsis 

 of Sars, under which, however, that observer appears to 

 describe several genera ; but, if we are to follow the new 

 arrangement of Hseckel in his recent reconstruction of the 

 Siphonophora, we must put it in the genus Halistemma, in 

 which he includes the Halistemma of Huxley, the Agalmopsis 

 punctata of Kolliker, and those forms of the Agalmopsis of 

 Sars whose tentacle-branches end in simple terminal filaments. 

 The creature or colony of creatures, according as its various 

 parts are regarded as organs or individuals, consists of a long 

 flexible stem, along which the various structures (organs or 

 individuals) are distributed in an irregular manner without 

 definite nodes and internodes. The stem presents a division 

 into an anterior shorter and a posterior longer portion, called 

 respectively the nectosome and the siphosome. The necto- 

 some is the locomotory part of the creature and is that portion 

 of the trunk which bears the swimming-bells, and after being 



