92 



EXPLANATION OF PLATE XIII. 



Fig. 1. Represents Xanthidium claviferum, discovered in a gun-flint: it has a hollow 

 oval body, with the tentacula gradually dilating from the base towards the 

 apex, where they terminate in irregularly stellated processes ; the tenta- 

 cula longer than the diameter of the body, and about twelve to fifteen in 

 number. Size jfoth of an inch in diameter. 



Fig. 2. Found also in a gun-flint. Similar to Xanthidium spinosum, but bears a de- 

 pressed line or division round the body. Size j^jth of an inch in diameter ; 

 the tentacula terminate in an acute point, and amount to about twenty- 

 five in number. 



Fig. 3. This species is like Xanthidium spinosum (See Plate, VIII. fig. 5, Vol. i.), but 

 is not longer than one-third of the diameter of the body, and appears to be 

 terminated at the extremities much less acutely, as is obvious on com- 

 paring the two figures. The size is ^th of an inch in diameter. I 

 have seen several specimens similar to this from the same locality : 

 the drawing is taken from the largest. 



Fig. 4. This species is very similar to X. crassipes, although the tentacula are neither 

 so numerous round the circumference nor so broad, and they do not exceed 

 one-fourth of the diameter of the body, while in the specimen figured by 

 Mr. White, they are equal to one-half the diameter. The measurement 

 is about ^ th of an inch from opposite extremities of the tentacula. 



Fig. 5. Similar to X. tubiferum-recurvatum, and measures from opposite extremities 

 of tentacula about ^gth of an inch. This specimen is remarkable for its 

 having the tentacula distorted or bent from the plane of direction, which 

 is another proof of the flexible nature of their substance. It may further 

 be observed that the apices of those organs assume no regularity of form — 

 they appear to be split in different ways, as if by accident. 



Figs. 6 and 7. Represent two specimens of the same species, but from diffe- 

 rent localities. Fig. 6 is from the Mediterranean, being found in the 

 residuum of a Pinna shell from that locality -. it was treated with muri- 

 atic acid to procure the siliceous shells attached to it. It appears 

 identical with the recent Xanthidium from New York, as figured at PI. 

 VIII. Vol. i. : the tentacula are terminated in the same manner, but are 

 not so long ; the size is ^th of an inch in diameter, and on the under side 

 is an appendage similar to the neck of a flask, a peculiarity I have likewise 

 occasionally observed in some fossil species. Fig. 7 was discovered in the 

 Thames mud in company with figs. 3, 4, and 5, but is much smaller, 

 being only 3$j,th of an inch in diameter. ' 



