838 " THETIS " SCIENTIFIC RESULTS. 



The hydrothecse are tubular, gradually bending outwards,- 

 Their adcauline wall is altogether adnate to the pinna, except 

 for a distal moiety, comprising little more than the adcauline 

 tooth. Exceptionally, a slightly larger portion is free, and this 

 generally on the stem. Also where several regenerated margins 

 have succeeded each other within the old margin, as often 

 happens, it appears as if a lai-ger portion were free ; but, as a ■ 

 rule, there is little variation, virtually the entire adcauline wall i 

 of any primary hydrotheca being adnate. Tlie margin of the 

 hydrotheca is divided into three equal and equidistant teeth, one 

 adcauline, central and projecting, the others forming an abcau- 

 line lateral pair, which scarcely project beyond the line of the- 

 abcauline wall. The teeth are sepaiated by deep embayments. 

 The operculum has three flaps. The hydrothecal walls are- 

 strongly developed ; the abcauline terminates at the aperture in 

 a knob of chitin, and the cavity of the hydrotheca is cut off from 

 that of the stem by a horizontal base, from the inner corner of 

 which very short chitinous supports project downwards. 



The soft parts are poorly preserved, but these points were dis-- 

 tinguished : — A single tube of ccenosarc runs throughout the 

 colony, and from it the hydranths are given off on short branches. . 

 The hydranths, which enter through the anterior half of the base 

 of a hydrotheca, have about fifteen tentacles, and possess a small 

 blind-sac, from which proceeds a protractor muscle attached to ■ 

 the distal half of the abcauline wall. 



Gonosome. — The gonangia are borne on stem, , branches, or 

 pinnae, but are most common on the last. They arise from the 

 anterior of these, immediately beneath a hydrotheca, and lie so 

 closely against the pinna that the adcauline portion of the - 

 gonangium becomes hollowed to fit it, as in the case of Theco- 

 cladiuni Jiabeilum, AUman, while the margins of the gonangium- 

 show more intimate adaptation to the outlines of hydrothecse • 

 and internode. The profile is very diflPerent as seen in frontal and 

 lateral aspects {cf., Plate Ixxxviii., figs. 1 and 2). No distinct stalk 

 is present, and in the former view they appear as much elongated ' 

 (length three times maximum breadth), slightly club-shaped 

 bodies, with a small circular aperture which lies a little within 

 the upper margin and faces the observer. In lateral aspect, the ■ 

 profile is wedge-shaped, for the gonangium widens gradually 

 towards the summit, the adcauline distal edge bein^g produced in > 

 a short angle along the stem, while the abcauline edge is replaced 

 by the aperture, termino-lateral in position, facing upwards and 

 outwards, placed upon a short narrow tube with trumpet-shaped" 

 lip, the tube set in a shallow depression of the gonangium wall. 

 Faint traces of annulation sometimes occur, especially on the 

 distal half of the gonangium. In the cases where* the preserva- - 



