ITydvactinia, Parlcoria, and Stromato])ora. Gl 



^('thcr, niiiiarall('lt'(l in tlic structurt' ot' recent or fossili/.nl 

 Fdraminitera. 



Ijjvstly, the general honiogonoity of the ti.s.suc-fibrc in 

 Pttr/rcn'a is incompatible with the general or partially cored 

 fibre of sponges, to say nothing of its uniformily in size, as 

 before mentioned. It may be a question, by-and-by, when wc 

 come to Sfroimifopora, how far the radial tubes of Pdrkcrin 

 extended continuously in a vertical direction — that is, whether 

 they went beyond two successive lamiiue. If they were like 

 those of Tit/u'/tora miu^ica, they did not do so ; for although 

 those of 2\ mnsica appear to be continuous through a great 

 many successive laminaj, they will, if examined interiorly, be 

 found, as before stated, to possess a diaphragm close to each 

 lamina, which thus divides them into a great number of parti- 

 tions. Again, in the fossil species Ihjdractiaia pllocena the 

 radial tubes seem, from their length in the vertical section, 

 (fig. 7) to pass through several successive lamina} ; but <mi 

 reference to the illustration (fig. 9) it is evident that this may 

 be explained by their openings respectively in the floor and roof 

 of the interval or chamber (fig. 9, d^d) being frequently o/>y;r>- 

 site each other. So in Stromatoiwra, the vertical continuation 

 of the tubes is no indication of their having been continuously 

 hollow, any more than in Tidnjwra musica. However, in the 

 hydroid polyp Tuhularia indivisa the tubes are not only 

 continuously hollow for 6 to 12 inches, but separate, and equal 

 in diameter to those of Tuhipora musica, viz. l-16th of an 

 inch (llinck's Brit. Ilydr. Zoophytes, p. 115, pi. xx.). 



Species o/Parkeria. 



Besides the spherical foi-m of Parkeria, which, for distinc- 

 tion sake, may be named P. sjducrica, there is a bossed form, 

 in which the surface projects into a number of large, circular, 

 convex eminences, which might be designated P. nodosa. In 

 structure, the latter appears to differ from the former in the 

 wavy disposition of its laminaj (which, of course, follow that 

 of the surface) from the very centre, showing that this form is 

 concurrent with the commencement of its growth. There is 

 also another fonn in the Cambridge Greensand, of which my 

 friend Mr. W. J. Sollas gave me specimens ; and this fs cir- 

 cular compressed — that is, biconvex or lenticular. It might be 

 designateu P. compressa. Possibly there are other varieties, 

 which may hereafter be recognized. 



LOFTUSIA (fig. 18). 

 As regards Loftusia {L. pcrsica, Brady), which appears to 



