84 THE VOYAGE OF H.M.S. CHALLENGER. 



connective tissue, which surrounds the canal, some scattered, rather large, more or less 

 straight spicula are found, the ends of which are frequently provided with smaller 

 processes or spines. The madreporic tubercle is divided by the medio-dorsal mesentery 

 into two halves, each being flat, of an ovate form, and strongly concave along its middle, 

 and having a length of about 4 - 5 mm. ; the free surface through which the ambulacral 

 system communicates with the peritoneal cavity is uneven on account of a number of 

 wrinkles and papillae. ■ The large and branched ambulacral cavities of the pedicels, which 

 lie enclosed within the body-wall, give off each a short, wide, somewhat branched csecal 

 prolongation or vesicle, which depends freely into the peritoneal cavity (PL XLI. fig. 3). 

 The processes of the dorsal as well as of the ventral lateral ambulacra communicate 

 exclusively with these branched vesicles. The reproductive organ is composed of two 

 fascicles, each consisting of about twenty larger and smaller oval caeca ; those fascicles 

 communicate with a short, wide tube on each side of the medio-dorsal mesentery, which 

 tubes pass into a common efferent duct which opens externally by a pore situated about 

 25 mm. from the anterior extremity of the body. 



Ilyodcemon, Theel. 

 Ilyodcemon, Th^el, Preliminary Report on the Holothuridse, pp. 11, 12. 

 Tentacles fifteen, rather large and non-retractile. The lateral ambulacra of the 

 ventral surface with large pedicels, apparently disposed in a double row all along each 

 side of that surface. The odd ambulacrum naked. The dorsal surface with a crowded 

 series of very numerous, retractile, slender, rather long processes, disposed in three or 

 four irregular, close-set rows all along each of its ambulacra. Integument with numerous 

 wheels and dichotomously branched bodies. 



Ilyodcemon maculatus, Theel (PL XVI.). 



Ilyodcemon maculatus, TWel, Preliminary Report on the Holothuritlse, p. 12. 

 Body elongated, of almost equal breadth throughout, about thrice as long as broad. 

 Mouth anterior, almost ventral. Anus posterior, subdorsal. Tentacles of nearly equal 

 size, with large circular discoidal ends, bearing round their edge small rudimentary 

 processes ; the ventral tentacles of one individual a little smaller. Pedicels of each side 

 of the ventral surface varying in number from about twenty-nine to about eighteen ; 

 the posterior pairs smaller. Pedicels of the inner row apparently alternating with those 

 of the outer. Processes of each of the dorsal ambulacra very numerous, about one 

 hundred and forty to one hundred and fifty, cylindrical or fusiform ; the largest as long as 

 the breadth of the body. Back naked along its middle between the processes of both the 

 ambulacra, except anteriorly a little behind the tentacles, where there is a small genital 

 process. Integument thick and soft, with three sorts of calcareous deposits very 



