198 Mr. II. J. Carter on 



the head and stem are composed of firm whitish cartilage, and 

 the nodosely tuberculated surface of the former covered by the 

 Halisarca tends greatly to obscure the position of the openings 

 of the Ascidian. Internally the head is smooth, corresponding 

 with the form of the Ascidian which it contains, so all the rest 

 must be viewed as the test, connected only with the Ascidian 

 itself by vascular extension from the latter, which here most 

 strikingly manifests its presence by two large vessels (? artery 

 and vein) which, side by side, longitudinally and centrally 

 extend throughout the stein. But the most remarkable part 

 of the stem is that, being almost entirely composed of the 

 white or colourless cartilage, it has imbedded in its structure 

 a thin cylindrical layer of reticulated, anastomosing, keratose, 

 solid, laminated, amber-coloured fibre, so similar to that of a 

 keratose sponge, that, if the two were placed together, it 

 would be almost impossible to distinguish between them. 

 This is situated just inside the circumference of the stem in 

 the midst of the white cartilage, where, by its amber-yellow 

 colour, it contrasts strongly with the latter. It extends from 

 one end to the other of the stem, to which it appears to 

 be confined, disappearing equally towards the head and in 

 the branches of the root-like expansion. Nowhere does the 

 presence of the Halisarca appear to influence the form of the 

 test, which is as smooth over the uodosely tuberculated 

 head as it is over the even surface of the cylindrical 

 stem. How far the Ascidian itself may be identified with 

 Prof. Herdman's Boltenia pachydermatina (' Challenger ' 

 Keports, pt. xvii. p. 89) I am not prepared to say ; but as I 

 find specimens of both in Mr. Wilson's collection, I can with 

 confidence state that there is considerable difference between 

 the forms of the tests and the composition of their stems gene- 

 rally. That which corresponds to the description of Boltenia 

 pachydermatina is not covered with Halisarca^ while the 

 smooth, wrinkled, and horn-like corrugated stem presents no 

 keratose fibre, but is charged with little calcareous spicules 

 extending inwards for about l-180th in. ; inside which the 

 cartilage and the two longitudinal vessels are the same as in 

 my Boltenia australiensis. In general form, composition, and 

 appearance the spicule is like that of the Alcyonaria, while 

 it more particularly resembles that from the stem of Boltenia 

 reniformis, as represented by the late Prof. Quekett (' Lec- 

 tures on Histology,' 1852, p. 264, fig. 148) ; that is, consist- 

 ing in its most perfect state of a short thick shaft, terminated 

 at each end by a rosette of five globular tubercles arranged 

 quincuncially, the whole about 8 by 7-6000ths in. in greatest 

 dimensions. 



