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



must have had a maximum breadth of about 4 mm. The whole of the body-disc has an 

 almost uniform thickness of about 0'25 to 0"33 mm., and is slightly translucent through- 

 out, with the exception of the parapodial insertions. The margin is very finely notched ; 

 the colour uniformly greyish -yellow. The back bears a gently ridged longitudinal 

 swelling (fig. 3), and at its sides five pairs of oval prominences, which represent the 

 parapodial insertions on the ventral surface. No trace of suckers could be detected. 

 The slightly developed parapodia (fig. 2, p) are disposed in two longitudinal rows, somewhat 

 nearer the median line than the external margin, and the first pair is at an unusually 

 great distance from the anterior end. The mouth (ph.) and cloacal papilla {cl) are also 

 very small, and are situated at the extremities of a slight longitudinal ventral eleva- 

 tion representing the dorsal median ridge, and much nearer the margin of the body 

 than the parapodia. 



The smaller specimen is about 5 mm. in length, and is so completely bent in 

 ventrally, that it has the form of a boat. 



In the form of the body and in the absence of suckers this species seems closely 

 related to Myzostoma folium (Report, pi. iii). 



Found on Antedon marginata, P. H. C, from Station 208 of the Challenger 

 Expedition. 



77. Myzostoma heardi, n. sp. (PI. III. figs. 1-4). 



I have named this species in honour of the successful investigator of the develop- 

 ment of the Myzostomida, Dr. John Beard. In every respect this form very closely 

 resembles Myzostoma j^sfi'tao^ii'd (Report, No. 61), with which I at first regarded it 

 as identical. It causes on Antedon flexilis, P. H. C, the same deformity as the above 

 species on the arms of Pentacrinus alter nicirr us, P. H. C. The single specimen before 

 me was obtained from the same Antedon fiexilis (Statioii 192, Challenger Expedition, 

 Arafura Sea) as the above described deformed pinnule with Myzostoma willemoesii. 



The arm in question (PI. III. figs. 1, 2) has been modified in the neighbourhood of 

 a syzygy. The enlargement is most marked in the joint just below the syzygial one ; 

 and it extends upwards, not only on to the hypozygal (a), but also on to the epizygal 

 joint, all three being somewhat expanded on the right side. The expanded portions are 

 tubercled, and the most swollen joint, the one before the syzygy, has on the side a smaU 

 funnel-shaped aperture (fig. 2), which leads into the cavity of the cyst. A second 

 much larger opening is found, however, on the ambulacral side (fig. 3). 



In this inconspicuous cyst, which would quite have escaped the notice of a less 

 accurate observer than my friend Carpenter, lay the brown Myzostoma represented in 

 fig. 4 from the ventral surface. There was certainly no second individual within the 

 cyst. 



