376 PROF. E, A. MINCHIN ON THE BRITISH [DeC, 13, 



Haeckel has given a plate (Monographie, pi. 18) intended to 

 ):epresent the t'orm-vaiiations of L. variabilis, but, in my opinion, 

 the greater number of his figures are untrue to nature. The 

 most charitable interpretation that can be put upon this plate is 

 to suppose that many of the specimens figured are incorrectly 

 determined and are not L. variabilis at all. Thus fig. 12 is 

 evidently a Clathrina, and fig. 1 5 is either a contracted Clathrina, 

 probably coriacea, or possibly a specimen of variabilis in which, 

 owing to rough usage, all the oscular tubes have been knocked 

 off. Fig. 2 probably represents some of the Sycons which, as I 

 laave stated below, are commonly found growing in company with 

 L. variabilis, and the same interpretation possibly applies to 

 figg. 1 and 3, the latter being contracted ; what figg. 10 and 13 

 may be I should not like to assert, but they are certainly not 

 specimens of variabilis. On the other hand, figg. 8 and 14 are 

 probably specimens of variabilis, which owe the extraordinary 

 curves exhibited by their oscular tubes to shrinkage as the result 

 of desiccation. The imaginative figures given by Haeckel on this 

 and other plates are lesponsible for the general opinion, far from 

 being true, that any Ascon may assume any form in which any 

 other species of Ascon occurs. 



As compared with other species, I find a tendency in variabilis 

 for the oscular rim to be of greater length. In young specimens 

 this is sometimes very marked indeed. The body- wall of variabilis 

 is generally thicker and stronger than in L. complicata, and the 

 sponge is evidently hardier, as seen fi-om the more exposed 

 situations in which it grows. 



(b) Characters of the /Spiculation. 



(a) Triradiate and Quadriradiate Systems. — (1) The ordinary 

 triradiates (text-fig. 94, figg. 10«-10c, &c., p. 377) have the rays 

 slender or of moderate thickness and tapering gradually to sharp 

 points. The unpaired ray is straight, and distinctly shorter than, 

 very rarely as long as, the paired rays. The unpaired angle is always 

 much greater than 120°. The paired rays usually show a distinct 

 double curvature, each ray curving first backwai-ds, then forwards 



Explanation of Text-fig. 94 (opposite). 



Spicules of Leucosolenia variabilis. 



IPigg. lOa-lOjD. Spicules of a specimen with monaxons not reaching a large size, 

 from Roscoif. a-c, ordinary triradiates; d, e, T-shaped triradiates (in this 

 specimen not greatly thickened) ; f, g, brackets ; h, i, ordinary quadriradiates ; 

 J, bracket with long gastral ray ; Jc, I, straight slender monaxons ; m-p, ordinary 

 curved monaxons. — Figg. lla-11^. Spicules of another specimen from Roscoft", 

 in which all the monaxons are small, a, b, triradiates ; c, T-shaped quadri- 

 radiate ; d, ordinar}"^ quadriradiate ; e, straight slender monaxon ; J] g, curved 

 monaxons.— Figg. 12 a-\'2,j. Spicules of a specimen from Roscoif in which the 

 monaxons vary up to a large size, a, triradiate ; 6, quadriradiate; c, <^, straight 

 slender monaxons ; e-j, curved monaxons. — Fig. 13. Monaxon of large size from 

 a, Roscoif specimen. 



