and Nomenclature of Sponges. 163 



families are determined by the presence or absence of certain 

 kinds of spicules. Thus, in the more inconspicuous siliceo- 

 spicular Sponges, the presence of bianchorate or birotulate spi- 

 cules characterizes ^sjoereWoe, and of stellate spicules Tethyadw^ 

 both kinds are absent in HalicJwndriada;. Now Dr. Bower- 

 bank's own specific descriptions show that some of his genera 

 contain species belonging to two, and some to all of these three 

 families ; yet he does not use the presence or absence of these 

 spicules to divide the genera into sections, though in his pre- 

 liminary chapters he shows that he believes the stellate and 

 bihamate spicules have an important use in the habits and 

 economy of the animal. 



The following analyses of these genera show the details of 

 this statement : — 



Almost all the Dictyocylindri belong to Halichondriada^ ; 

 but D . fascicidaris and D. stujwsus have stellate spicules, and 

 belong to Tethyadaa. 



Hymeraphia vermicularis and H. davata belong to Hali- 

 chondriadge, and H. verticillata and H. stelUfera are Tethyadge, 

 having stellate spicules. 



The three species of Hymedesmia^ for example, belong to 

 three families — H. radiata to Halichondriadte, H. stellata to 

 Tethyadse, and H. zetlandica to Esperiad^. 



Six out of the eight species of Microciona have anchorate 

 spicules and belong to Esperiadee, and the others, M. Imvis 

 and fallax, to Halichondriadse, having only fusiform spicules, 



Of the genus Hymemacidon, which contains thirty-nine 

 species, by far the greater part belong to Halichondriadte, one 

 to Clioniadas ; but there are scattered among them (why, I can- 

 not comprehend) nine belonging to Esperiadaj, as (9) H. 

 perarmatus, {16) H. variantia^ (16) -ff. macihnta^ {24t)H.lingulay 

 (25) H. floreum^ (27) H. plwnosa, (28) H. jecuscxdmn^ (33) H. 

 subclavata, and (37) H. paupertas^ — one, (39) H. Bucklandi^ 

 to Tethyadge. 



Of the twenty-eight species of Halichondria more than half 

 do not belong to Halichondriad^e : thus (8) H. angidata is a 

 Tethyad; (9) H. corrugata, (10) H. Thompsoni, (11) H. for- 

 ctpis, (14) H. 'inc7'ustans, (15) H. Candida, (16) H. Irregularis, 

 (17) R. Dickiei, (18) H. Pattersoni, (19) H. pulchella, (20) H. 

 Ingalli, (21) H. scandens, (22) H. Batei, (23) H. gramdata, 

 (24) H. Hyndmani, (25) H. nigricans, (26) H. alhula, and 

 (28) H. inornatus belong to Esperiadse. 



Isodictya is the great magazine genus of the work : it con- 

 tains no less than forty-three species ; about two-thirds of 

 them belong to the family Halichondriadte. The following—. 



