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



Since the triradiate systems lie in the wall of a hollow cylindei', 

 the thi'ee i-ays are never in the same plane, but are disposed in 

 such a manner that if the spicule be viewed in a direction cor- 

 I'esponding to the axis of the unpaired ray, the two lateral rays 

 appear to meet at an angle less than 180° on the gastral side, 

 gi-eater than 180° on the dermal side. This is an important fact 

 to bear in mind when studying the spicules in prepai-ations. If 

 the spicvile be lying on the slide with its dermal face uppermost, 

 then the points of the three rays touch the slide, but their 

 junction is raised off it ; hence the spicule appears from this 

 aspect peifectly symmetiical, with two lateral raj^s of equal length 

 and similar curvature, but each of the three rays is slightly fore- 

 shortened. If, on the other hand, the spicule be lying on the 

 slide with its gastral face uppermost it may lie so as to appear 

 symmetrical, but more usually it is found lying with one lateral 

 ray and the posterior ray flat on the slide, the other lateral ray 

 pointing obliquely upwards. Hence when the two rays which 

 lie flat are in focus the third ray is out of focus, and when drawn 

 with the camera it appears foreshortened, giving the spicule an 

 asymmetrical appearance. To this fact is due the foreshortened 

 appearance of one of the two lateral spicule-rays in many of 

 my drawings, especially of L. hotryoides, in which the thickened 

 T-shaped triradiate systems are very concave on the gastral face. 



Y. Description of the Species. 



1. Leucosolenia complicata. 



Spongia complicata Montagu, 1812, Wernerian Memoirs, ii. 

 p. 97, pi. ix. figg. 2, 3. 



Spongia hotryoides pars Grant, 1826, Edinb. New Phil. Journ. 

 i. p. 169. 



Grantia hotryoides pars Fleming, 1828, Hist. Brit. Animals, 

 p. 525. 



Grantia hotryoides pars Johnston, 1842, Brit. Spong. and Litho- 

 phytes, p. 178. 



Leucosolenia contorta pars Bowerbank, 1866, Mon. Brit. Spong. 

 ii. p. 9 ; 1874, iii. pi. iii. figg. 5-10. 



Leucosolenia hotryoides Gray, 1867, P. Z. S. p. 555. 



Leucosolenia fahricii O. Schmidt, 1869, Mitth. natui-wiss. Yer. 

 Steiermark, ii. p. 91. 



Leucosolenia fahricii 0. Schmidt, 1870, Grundz. Spong.-Faun. 

 Atl. Geb. p. 73. 



Oly^ithus hispidus Haeckel, 1870, Jena. Zeitschr. v. p. 237. 



Olynthtis pocilhim Haeckel, 1870, 1. c. p. 237. 



Leucosolenia amoehoides Haeckel, 1870, 1. c. p. 243. 



Leucosolenia (Lettcelia) complicata Haeckel, 1870, 1. c. p. 243. 



Leucosolenia fahricii Haeckel, 1870, 1. c. p. 243. 



Asculmis seu Ascandra armata Haeckel, 1872, Kalkschw. 

 pp. 77-79, pi. 13. 



