[DAWSON] FOSSIL SPONGES AND OTHER ORGANIC REMAINS 



103 



This is one of the most aluuuhnit species ;it Little Metis. There can 

 be no hesitation in p!acin<>; it in the genus Frotosporujla, since the same 

 arrangement of the spicuhir mesh-work is present in it as in the type of 

 tliis genus. In the earlier examples of the genus, liowever, tlie presence 

 of anchoring-spicules was not recognized, owing, no doubt, to their imper- 

 fect state of preservation, and this feature ma}' now be reckoned as one 

 of the generic characters. In the jjresent species, however, these anchor- 

 ing-spicules were ver}' peculiar, and seem to be rays of a cruciform 

 spicule, which were bent upward and lengthened, forming a stalk for 

 the sponge. This would give a firm attachment, and adapt itself to the 

 gradual rise of the bottom to which the sponge was attached. The 

 mechanical pro]>erties of such an arrangement of spicula are obviously 

 well suited to effect their purpose. 



Some further remarks on the lyssakine character of Protosponyia 

 will be found in the paper of 1889, and the more recent collections also 

 show that the skeleton spicules, at first small in the young specimens; 

 grew in length, l)y additions to the ends of the rays as the body increased 

 in size. 



2, — Protospongia mononema, Dawson. 



(Figs. 6, 7 and 8. PI. I., Figs. 2 and 3.) 



Fig. 6.— Protospongia Fig. I.—Protosjjongia mononema. Cruciform and 



mononema. Restored. protective spicule.s, x 5. 



General size about one inch in diameter, originally globular but now 

 flattened. Body spicules cruciform and more slender than those of 



