GEODIA LOPHOTRIAENA. 



187 



This table shows that these two species, although very similar in many 

 respects, differ considerably in others. The difference in the shape of the body, 

 the thickness of the cortex, and the length of some of the megascleres might be 

 considered as due to differences of age or to differences in individual adaptation. 

 That plagiotriaenes are present in G. lophotriaena and not mentioned as occurring 

 in G. sphaeroides would, in itself, also hardly be sufficient for systematic distinc- 

 tion, because their relative abundance varies in the different specimens of G. 

 lophotriaena and because according to Topsent * only ortho- plagio-triaenes 

 or only dichotriaenes or both these kinds of spicules may be present in another 

 species of Geodia, G. conchilega. That Thiele and Lindgren describe the pro- 

 clades of G. sphaeroides (G. arripiens) as protriaenes, while they are mesopro- 

 triaenes in G. lophotriaena, is also of but little importance, since it is known that 

 mesoprotriaenes have often been described as protriaenes. That lophotriaenes 

 with more than two end clades occur in G. lophotriaena, besides the ordinary 

 dichotriaenes, while only true dichotriaenes with two end clades have been ob- 

 served in G. sphaeroides, might be a more important difference, if one could only 

 be convinced, as I am not, that such lophotriaenes are really altogether absent in 

 the latter. Greater importance than to this is, in my opinion, to be attached to 

 the differences in the clades of the mesoprotriaenes (protriaenes) and anatriaencs, 

 which are very stout and, in the mesoprotriaenes (protriaenes), often partly 

 reduced in length and irregular in G. sphaeroides, but regularly developed to their 

 full length and slender in G. lophotriaena. Still more important than these 

 differences are those of the sterrasters and large eu asters. The sterrasters are in 

 G. sphaeroides twice as large as in G. lophotriaena, while there is no corresponding 

 difference in the size of the other spicules and the whole body. The large euastcrs 

 are in G. sphaeroides oxysphaerasters, 36-50 /i in diameter, with a large centrum 

 and stout, spined rays; in G. lophotriaena oxyasters, 15-41 /< in diameter, with a 

 very small centrum or no central thickening at all, and perfectly smooth, slender 

 rays. These differences, particularly the last named, appear to be germinal 

 in nature and, particularly when taken together with the others, in themselves 

 unimportant, quite sufficient for specific distinction. 



' E. Topsent. ^Itude mongraphique des spongiaires de France I. Arch. zool. exper., 1894, ser. 3, 

 2, p. 326. 



