ZOOLOGY. 341 



Leptomedusse, from the velum." It is concluded that Limnocodium " will 

 hold a position intermediate between the Leptomedusie and the Tracho- 

 medusae ; but as the greatest systematic importance must be attached 

 to the structure and origin of the marginal vesicles, its affinity with the 

 Lejitomedusai must be regarded as the closer of the two." 



ECHINODERMS. • 



A NEW ORDER OF HOLOTHURIOID ECHINODERMS.* 



Quite a number of remarkable forms hav^e been procured within the 

 last live years at great depths of the ocean in various parts of the world, 

 and these have been recently brought together by Hjalmar Theel in one 

 group, diflerentiated as an " order " closely related to the Holothurioidea. 

 These newly discovered forms essentially resemble the Holothurioids in 

 general structure. It is noted, however, that the Holothurioids are 

 mostly fusiform or cylindrical in shape, although some {e.g.,F.solus and 

 Cuvieria) are most decidedly bilateral ; the radiate symmetry prevails so 

 far externally that the five radial ambula<*ral vessels and their api>endages 

 are generally similar, or nearly so, and run symmetrically at equal dis- 

 tances from one another from the anal to the apical pole, and they may 

 be even used indifferently for the jnirpose of progression ; but, never- 

 theless, of these five ambulacra, three — constituting the trivium — are ven- 

 tral, and the other two — the bivium — are dorsal. While such is the rule 

 however the exceptions are such as to comjiel us to be cautious, 

 lest we place an undue value on deviations even much less than those 

 recognized as occurring in forms universallj" conceded to be true repre- 

 sentatives of the order. 



In the newly discovered forms the body is always " distinctly bilat- 

 eral," (1) '< the lateral ambulacra of the trivium bearing large, slightly 

 retractile pedicels, disposed either in a single row, or sometimes in two 

 rows, along each side of the ventral surface, and sometimes with another 

 series of larger highly elongated not retractile processes placed exter- 

 nally and above the pedicels ; pedieels of the two lateral ambulacra 

 symmetrically arranged, being more or less distinctly opposed across the 

 ventral surface " ; (2) "the odd ambulacrum naked, or very seldom with 

 a few rudimentary pedicels"; (3) "bivium i)rovided with very long, not 

 retractile processes, often disposed in one or more rows along each of its 

 ambulacra, and more or less distinctly opposed across the dorsal surface, 

 or with only a few rudimentary ones in its anterior jiart, or with a single 

 very large one resembling a broad, brancheil or unbranched lobe, and 

 near to it some small j^apillfe;" (4) there are "no respiratory trees;" 

 and (a) the integument is " naked, spiculous, or plated." Such are the 

 characteristics common to the forms. While the ordinal value of this 

 type may perhaps be generally disputed, the forms are of no little in- 



* Hjalmar Tli<5el. The Elasmoiioda, a new order of Holotliuridea.. 2^ature, vol. xxi, 

 pp. 470-473, March 18, 1880. 



