230. DE. ni>'DE AND ME. UOLMES ON SPONGE-EEMAINS 



Modified Stellate and Calthrops Spicules o/" Corticium. 



PI. XII. figs. 22-29. Spicules in whicli tlie number of rajs 

 A^aries from 3 to 14. In all the forms the rays are short, obtusely 

 2:)ointed, and frequently unequal in size in the same spicule. The 

 simple^t is a 3-rayed form (fig. 28) ; the rays are '03 mm. in length 

 by '0067 mm. in thickness. Fig. 27 represents a minute calthrops 

 spicule in which the rays are "026 mm. in length. Eig. 29 is also of 

 a calthrops type, but it has five rays, about '016 mm. in length. 

 In the other forms (figs. 22-26) the rays are more numerous, 

 ranging from 6 to 14, and the spicules exhibit a stellate arrange- 

 ment. The rays in these are short and obtuse, and appear very 

 different from those of ordinary stellates. The diameter of these 

 spicules ranges from •021 to "Ol mm. In their general appear- 

 ance they resemble spicules of Corticium ; and in a recent Adriatic 

 species, C. stelligerum, Osc. Sch. (Algier. Spong. p. 25, t. iii. 

 fig. 6 6), there are stellate and small calthrops spicules, somewhat 

 similar to these fossils. 



PI. XII. figs. 30, 31, 32.— Small spicules with from 4 to 7 

 rays, which do not radiate from a common centre but from a 

 short linear axis. The rays are elongated, pointed, and together 

 with the central axis are traversed by canals which open at their 

 extremities. In fig. 30 there are 4 rays, '075 mm. in length, 

 which are in different planes. In fig. 31 there are six subequal 

 rays, '0217 mm. in length, which form, as it were, a double 

 trij)od. In fig, 32 there is a short central curved axis with three 

 elongate rays at either end, and an additional ray starting from 

 the middle of the axis. The rays in this form are minutely 

 tuberculate, and "021 mm. in length. These spicules can only 

 provisionally be placed under Corticium, they may possibly 

 belong to some other tetractinellid genus. In Corticium stel- 

 ligerum, Osc. Sell., referred to above, there are some peculiar 

 stellates in which the rays are given off from a thickened or 

 elongate axis. 



Candelabra Sjncules of Plakina, Scliulze. 



Plalcina australis, n. sp. — PI. XII. fig. 20. Candelabrum with 

 slightly curved tapering shaft and at its summit numerous 

 curved rays, furcate at their ends. The rays are apparently 12 

 in number, and grouped in systems of four. Length of spicule 



