Knowledge of the Spongida. 357 



Hyahnema Sieboldii. The free ends of these spicules appear 

 to me to be always terminated by three recurved arms, although 

 they often look like two, which illusion can be corrected by 

 alteration of the focus. Moreover I have never been able to 

 detect any " forks " or trifid extended arms among them, 

 which seems to indicate that there are none, as in the cord of 

 Hyahnema ) since, when the two forms are together, which is 

 commonly the case in Geodta, Stelletta, and Tethya y the 

 recurved arms are so much more liable to be torn off by 

 catching in opposing objects than the extended ones, that some 

 of the latter are almost sure to be retained when the former 

 have all disappeared. As the cords or root-like appendages 

 which vary m number (? under four) have been broken off 

 close to the body in my specimen, I presume that this 

 was the case in Dr. Bowerbank's, as they do not appear in 

 his illustration ; nevertheless he states that they are " about 

 finch in length" (I.e.). The flesh-spicules, on the other 

 hand, are spinispirular in form (Spiralsteruchen, Sdt), with 

 long microspined rays, varying much in size, so that the 

 largest appear to be of a different kind ; but by careful exa- 

 mination the smallest can be traced by gradation into the 

 largest, as Prof. Sollas has described (pp. 443, 444, I. c), 

 when their microspination of course becomes more evident. 

 Here I would observe that, among the spicules which Dr. 

 Bowerbank in his description (/. c. p. 118) has considered 

 " extraneous " in Saville Kent's illustrations of Dorvilliaaga- 

 riciformis {op. et I. c.) are " figs. 16, 17, 18," which are so 

 much like the larger forms of fiesh-spicule in Thenea muricata } 

 to say nothing of Dorvillia, in which they occur abundantly, 

 that when Dr. Bowerbank adds that he observed u several in 

 a piece of epidermis " of Tethea muricata that he had mounted 

 Ci in 1855," among which was the quadriradiate form repre- 

 sented by Mr. Kent in his fig. 18, it does not seem unreason- 

 able to inter that they were not " extraneous." Indeed there 

 are four or more such in the microscopic fragment of the type 

 specimen that I have in my cabinet of slides. 



The next form that claims our attention is Wyvillethom- 

 sonia Wallichii=Tisiphom'a agariciformis = Dorviliia agari- 

 cijormis, because its spiculation is so like that of Tethea 

 muricata ; and of tiiis species I may safely say that scores 

 have passed through my hands, out of which the most perfect 

 type, although small, that I could select, is now before me j 

 hence I can speak more authoritatively about it than any 

 other. Wyvillethomsouia Wallichii chiefly differs from 

 Tethea muricata in possessing the agaric form, which is well 



represented in both Saville Kent's and Sir Wy ville Thomson's 



