434 Mr. H. J. Carter on new Sponges. 



Fig. 3. The same, central portion, drawn to a larger scale, viz. l-24tli to 

 l-1800th of an inch, to compare with the fossil one, fig. 37. pi. 9, 

 vol. vii. p. 126, Annals, 1871 : a, shaft or vertical arm ; hhbb, ho- 

 rizontal arms ; c, central canal ; d, subsequent layer added to 

 the original shaft. 



Fiff, 4, The same, portion of a horizontal arm much more magnified, 

 showing the original shaft, the spiniferous layer, and the rela- 

 tive size of the macro- and microspines : a, original shaft ; b, ad- 

 ditional or spiniferous layer ; c, macrospines ; d, microspines. 



Fiff. 5. The same, lateral view, nat. size. 



Fiff. 6. The same, to show sigmoid curve of horizontal arms and straight 

 shaft, nat. size. 



Fiff. 7. The same, podal (?) spicule, showing portion of shaft and anclior- 

 or, rather, grapnel-head, consisting of four recurved arms. 



Fiff. 8. The same, hexactinellid form, in which the shaft is continued on 

 into a fifth arm («) or straight spike. 



Fiff. 9, The same, hexactinellid form, where one of the recurved arms (a) 

 is prolonged after the manner and length of a shaft. Abnormal 

 form ? 



N.B. These three figures are all drawn to the scale of l-48th 

 to 1-1800 of an inch. 



Fiff. 10. The same, longest portion of shaft foimd with anchor-head at- 

 tached, nat. size. 



Plate XXII. 



Fiff. 1. Tethya zetlandica, n. sp., attached to the stem of Halichondria 

 ventilabrum, Johnston, nat. size : a, papiUse, small and closely 

 approximated ; b, stem of H. ventilabrum. 



Fiff. 2. The same, nat. size, half the specimen : a, papillae, here large and 

 separate. 



Fig. 3, The same, anchor-headed spicule of the base of fig. 1, to show, 

 a, the continuation forwards of the central canal towards the 

 point. Scale l-24th to 1-GOOOth of an inch. 



Fiff. 4, The same, fully-developed young one, nat. size, viz. l-16th of an 

 inch in diameter. 



Fiff. 5. The same, magnified about IG diameters, showing : — a, areolated 

 sarcode ; b, spicules, chiefly one-armed anchor-headed, of the 

 form given in fig. 115, d. 



N.B. This must be viewed merely as a diagram. It would be 

 almost impossible to give a facsimile of this beautiful object 

 with all its detail on this scale, 



Mff. 6. The same, earlier stage : a, defined margin of the ovule ; b, gra- 

 nular plasma ; c, spicules, now few and all acerate or without 

 heads, showing that the acerate is the fundamental form of the 

 spicule. 



N.B. The same remark applies to this figure : it must be 

 regarded as a diagram. To have introduced a shade for the 

 " granular plasma " would have confused the whole. 



Mff. 7. The same, still earlier stage of the ovule, viz. while it is imbedded 

 in the sarcode, now about l-400th of an inch in diameter : 

 a, cell- wall ; b, nuclear cavity (?) ; c, nucleated cellules ; d, nu- 

 cleated cellule, more magnified, showing contained granules, 



Fiff. 8. Halichondria simulans, Johnston • two sponge-animalcules in 

 zygosis ? : « a, bodies of sponge-animalcules respectively ; b b, 

 their necks or rostra in conjugation. 



