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



truncated mouths, they are directed upwards and bent towards the stem. Their length 

 reaches 0'6 to 0"7 mm. They stand in not very distinct spirals, still not so closely 

 crowded as in Mopsea encrinula. At the apex of the twigs they arise only from two 

 sides alternately. On the thicker twigs they still stand in spirals, but the individual 

 polyps are smaller and stand at wide distances from one another ; on the stem they are 

 still isolated, but in part can still be recognised as projecting papillae. Accordingly, on 

 the older part of the colony degeneration of the polyps appears to take place. 



The horny joints of the axis are, in the lower part of the stem, longer than the 

 calcareous joints, but soon become shorter, and already in the stem the calcareous joints 

 become double their length. In the branches and twigs the calcareous joints are more 

 than four times as long as a horny joint. In the stem the calcareous joints are slightly 

 compressed in one plane and distinctly fluted longitudinally ; sometimes the ribs between 

 the longitudinal furrows show sharp indented edges. 



The branches sometimes arise from the middle of the calcareous joint, more frequently 

 from the upper edge, where their first horny joint fuses with the horny joint of the axis. 



The spicules in the coenenchyma are prickly, lancet-shaped, often curved plates, with 

 strongly toothed edges and with sharp warts on the surface ; they are thickly placed and 

 give the surface of the coenenchyma a rough appearance. Length to breadth in mm. — 

 0-22-0-05; 0-12-0-08 ; O'lG-O-l ; 0-2-0-07 ; 0-18-0-06. 



In the polyps the plates became strong scales convexly bent on the surface, whose 

 lower edge is incised and whose toothed upper edge is overhung by sharp spines. 

 Height to breadth 0-08-0-16 ; 0-07-0-15 ; 0-05-0-22 mm. 



Colour in alcohol, yellowish-white. 



This species is excellently characterised by Lamouroux, and after his well-defined 

 characterisation of the genus it is not well possible to confuse it with a Melithaeidean. 

 He gives the diagnosis as follows : — " Rameaux greles, cyliudriques, presque filiformes, 

 avec dichotomies k chaque articulation ; polypes mamiUiformes dans les rameaux 

 superieurs, tuberculeux dans les moyens, superficieles dans les inferieures ; ecorce unie 

 sue la tige." The original specimens of Lamarck's Isis dichotoma in the Zoological 

 Museum at the Jardin des Plantes, Paris, agrees in all particulars with our specimens, 

 and it still has the original label attached to it, with the name written thereon in 

 Lamarck's handwriting. 



Gray's Mopsella dichotoma is, on the other hand, a Mclithseidean, as is sufficiently 

 evident from the description, and this is confirmed by Verrill when he says :— "I am unable 

 to find any generic differences between this species and those subsequently referred by 

 him to Melitella." 



Habitat. — Port Jackson, Australia ; depth, 35 fathoms. Three specimens. 



The Indian Ocean is given by Lamouroux as the place where the species was 

 found. 



