REPORT ON THE HEXACTINELLIDA. 281 



All the uncinates in Farrea occa are disposed at right angles to the surface, and thus 

 traverse the wall of the tube in a radial direction. The sharp external point does not, 

 however, penetrate the dermal membrane, but at most reaches it. The inner weaker, 

 and always pointed ends remain at some distance from the gastral membrane, varying 

 according to the relation between the length of the uncinates and the diameter of the 

 tube-wall. 



Besides the uncinates, parenchymalia are represented by simple oxyhexasters in more 

 or less abundant occurrence. In these the long smooth principal rays divide into two to 

 four ■^\ddely diverging, straight or gently curved terminals, half as long as the principals 

 (PI. LXXI. fig. 7). These oxyhexasters occur most abundantly in the subdermal and 

 subgastral trabecular space, but more sparsely in the middle layers of the tube-wall, even 

 between the chambers, without, however, being altogether absent (PI. LXXI. fig. 3 ; 

 PL LXXIII. fig. 2). They are embedded in the trabecular network itself, and I am 

 inclined to think that the formation of the trabeculse and their interconnection is of the 

 greatest importance in relation to the form of these spicules. In Carter's specimen of 

 Farrea occa the terminal rays of the rosettes were as a rule smooth and pointed, though 

 occasionally microspined and more or less " capitate." In the specimens which I 

 examined, on the other hand, there were never any traces of terminal knobs or discs on 

 the terminal rays of the rosettes, that is to say, of transitional forms between oxyhexasters 

 and discohexasters. I have, however, found specimens of Farrea in which the rosettes 

 were exclusively discohexasters, and these of an unusual type, but these were representatives 

 of a second species, namely, Farrea sollasii. Other specimens in which, besides the 

 oxyhexasters, discohexasters also occurred, belonged to a third species, Farrea vosmaen. 

 But if the different forms of rosettes as above noted really occur in one and the same 

 sponge, with distinct transitional types, then the forms which I have designated as two 

 distinct species, Farrea sollasii and Farrea vosmaeri may perhaps be regarded as 

 varieties of Farrea occa. I have not, however, as yet discovered such transitional forms, 

 and shall therefore meanwhile continue to regard these divergent specimens as distinct 

 species, until then- relation to Farrea occa be indisputably established. 



Besides the uncinates and the above mentioned rosettes, the parenchyma of Farrea 

 occa contains simple hexacts, of the same size as the rosettes, with smooth or rough, 

 straight, pointed rays, which usually exhibit a knob-like thickening on their point of 

 intersection. While these simple oxyhexacts have only a rare and isolated occurrence in 

 the upper younger portions of the Farrea stocks, they are abundant in the lower portion, 

 and in older stocks even numerous in the pedicel, and in the basal plate, within the 

 meshes of the dictyonal framework, where they are abundantly fused to the dictyonal 

 beams, so that by the gradual thickening of the rays, and their union with adja- 

 cent strands, they contribute to the thickening and compacting of the connected 

 skeleton. 



(ZOOL. CHALL. EXP. — PART LIII. — 1887.) Ggg 36 



