•_N-_> THE VOYAGE OF H.M.S. CHALLENGER. 



connective tissue part of the mantle, branchial sac, or other organ, and in one species, 

 Cynthia complanata, the spicules of the mantle are enclosed in very distinct membranous 

 sheaths (PI. XVII. figs. 4, 5, and 6), and curiously enough the sheaths of different spicules 

 are connected by continuations of their ends, so that the different spicules are united to 

 form a system of tube-like structures winding through the tissues of the mantle. 



As to the function of these calcareous spicules, I am not prepared to make any definite 

 statement. The first idea which presents itself is naturally that they are for the purpose 

 of giving strength and support to the organs in which they are present ; and this is 

 probably the correct explanation in the case of Culeolus. In that genus, on account of 

 the large meshes, and the want of fine longitudinal bars, the branchial sac is singularly 

 weak and fragile ; and the presence of the large branched spicules in the chief vessels 

 (very frequently placed at their points of intersection, so as to extend into several and 

 strengthen their junction) must materially add to the firmness and solidity of the organ. 



This, however, cannot apply in the case of Cynthia. There the branchial sac is as 

 strong as in most Simple Ascidians. And the species in which calcareous spicules have been 

 found seem to require support as little as any of the other species of the genus. Besides, 

 the spicules in Cynthia are, as has been pointed out above, very different in their 

 characters from those of Culeolus, and do not seem as if they would be nearly so suitable 

 for the purpose of strengthening a delicate organ. Consequently, I think it is probable 

 that they have a different function in this genus. 



In the Styelinse, besides a number of new species belonging to the large genera Styela 

 and Polycarpa, a specimen from deep water was collected, which has necessitated the 

 formation of the new genus Bathyoncus. The chief structural peculiarity of this form, 

 namely, its much modified branchial sac, has already been discussed above in connection 

 with Fungulus and Culeolus. 



Besides Bathyoncus mirabilis, the only deep-water Styelinse are two new species of 

 Styela — Styela bythia and Styela squamosa. The former of these has distinct languets 

 (PL XVIII. fig. 8) along the free edge of the dorsal lamina — which is usually a plain 

 membrane in the Styelinse — and the latter has only two well-marked folds upon each 

 side of the branchial sac ; but with the exception of these two points, Styela bythia and 

 Styela squamosa are fairly typical representatives of the otherwise shallow- water genus 

 Styela. 



In one of the new species of Polycarpa, the inconspicuous Polycarpa minuta, small 

 rod-shaped calcareous spicules are present, scattered through the prolongation of 

 the connective tissue of the mantle, which forms the covering of the polycarp (PI. 

 XXII. fig. 4), but they do not seem to be present in any of the other organs of the body. 



In the family Ascidiidaa, out of the four new genera formed for Challenger sjjecimens, 

 three, viz., Hypobythius, Corynascidia, and Abyssascidia are somewhat aberrant; while 

 the fourth, Pachycldcena, is closely allied to Ascidia. Corynascidia is undoubtedly 



