KErORT ON THE OPHIUROIDEA. 157 



Hemipholis. 



Hemipholis, Agas., "SIS.; Lyrn., 111. Cat. Mus. Comp. Zoo!., No. i., 1865. 



Disk, above, covered with rounded, rather thick scales, and with large united radial 

 shields ; below, naked. Disk slightly indented, at the base of each arm. Teeth. No 

 tooth papillse. Mouth angle extremely narrow, with a tooth at the apex, and a small 

 papilla at the outer corner. Side mouth shields touching each other, so as to form a 

 continuous ring round the mouth. Three short, tapering arm spines. Two genital 

 openings, beginning outside the mouth shields. 



This genus, scarcely to be separated by external characters from some species of 

 Amphiura that are naked below, presents considerable differences in the skeleton. In 

 the first place, there is no genital scale, but only a genital plate, with a clubbed 

 outer end and a strongly curved slender shaft. The mouth frames are much larger 

 than in Amphiura with prolonged wings, and a small but well-marked single peristomial 

 plate. 



The arm bones are wider, with thicker wings and a less marked forward projection 

 of the upper surface. Their lower surface presents an immense canal (PI. XL. fig. 9, t), 

 which rises in the substance of the bone like a high, wide arch, and changes the 

 usual position of the articulating peg (6). (See Plate XL. figs. 8-12.) 



Hemipholis cordifera, known long ago by the description of Bosc, is plentiful in the 

 harbour of Charleston, S.C., where it was collected by Professor Agassiz in 1852, and 

 was carefully examined in the living state by the late Professor H. J. Clark. Besides the 

 peculiarities already noted in the skeleton, the tentacles are papillose (PI. XLIV. figs. 

 13, r, 14, 15). The papiike, as well as the tip of the tentacle itself, are imperforate, as 

 appears in the section (fig. 14). The centre, however, is hollow, and contains a long 

 spiral, like a half partition, which is apparently muscular and doubtless aids in retraction. 

 Fig. 13 gives an excellent picture of a part of the under side of the living animal. 

 Between the points of the teeth, in three of the interbrachial spaces, may be seen a 

 white line, which is the edge of the mouth sphincter. The females were then (January) 

 full of eggs, one of which (fig. 16) is shown considerably magnified. 



The species is, I suspect, viviparous, as I found minute young, clinging to the arms 

 and disk of the adult. One of these, having a disk but half a mdlimetre in diameter 

 (PI. XL. fig. 12) displayed only the six primary back plates ((/, g'), and the beginning 

 of one interbrachial. There were as yet no radial shields, although the arms had already 

 ten joints. It was not until the disk was 1 mm. across that the beginnings of radial 

 shields were visible (fig. 11, I). Besides these there were not only the primary plates 

 (g, g') but one brachial and three interbrachial. It thus appears that radial shields, so 

 nearly universal among Ophiurans, are not special plates, but entirely homologous with 

 other disk scales, and by no means the first to appear. 



(ZOOL. CHALL. EXP. — PART XIV. — 1882.) O 21 



