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



3. Thouarella koUikeri, n. sp. (PI. XXI. fig. 5). 



A main stem, from which branches come off in different directions ; these again bear 

 lateral twigs on which the polyps are placed. The polyps are larger than in the preceding 

 species, and the calyx scales of the last row are pointed and lancet-shaped. In the best- 

 preserved specimen the main stem has a length of 150 mm., with at its base a thickness 

 of 2 mm. Here also the transverse section is oval, and there is a spiral twisting. 



The axis is in the lower part calcareous, brittle, and becomes softer and flexible 

 towards the apex. From the stem, branches arise at different heights ; these, as in the 

 preceding species, come off in three directions. They are, however, differently developed ; 

 on one side they remain short, on the two other sides, at angles of about 60° to the first, 

 they develop into long branches, which attain the strength of the main stem. At the 

 same time they bend themselves away from the main stem, especially in one direction. 

 Owing to this condition the colony attains a more bilateral structure ; designating the 

 side of the stem on which the short branches arise as dorsal, and the opposite side as 

 ventral, then one can distinguish dorsal and ventro-lateral or side branches. The dorsal 

 branches are always simple, 10 to 25 mm. long, flexible at the end, and directly bear the 

 polyps. The lateral branches, on the contrary, attain a strength which, especially in the 

 lower part of the colony, equals that of the main stem, and reach a length of 80 to 100 mm. 

 They themselves ramify in a similar manner to the main stem, giving off dorsal and 

 lateral twigs, which are generally soft and flexible, the lateral twigs may finally again 

 bear lateral twigs, while here the dorsal ones are wanting ; the dorsal ones are also wanting 

 at the ends of the lai'ger branches. 



The polyps are placed on all the finer twigs, as in the foregoing species, arising in 

 three dii'ections at different heights, so that they surround the stem in short spirals. 

 Their form is pear-shaped. There are eight transverse rows of scales present. These 

 have a convex upper edge ; the surface is provided with longitudinal ribs, diverging 

 above, of which a middle one is the most developed ; in the last row the middle rib is 

 very strongly developed and projects at the end as a point, above the edge of the scale, 

 which is higher than it is broad. 



As in the preceding species five dorsal and lateral longitudinal rows of scales may be 

 distinguished, and two ventral ones, which are thin, transparent and ribless. The 

 opercular scales are strongly concave, the dorsal ones pointed, with serrated edges, the 

 ventral ones small, scale-like, covered by the broad lateral ones. 



Scales of the calyx. — The scales of the uppermost row are higher than they are broad, 

 in the middle line there arises from the nucleus a greatly serrated keel, prolonged into a 

 spine which projects beyond the edge of the scale, the lateral edges are finely toothed. 

 Height to breadth, 0'62 to 0"54 mm.; the succeeding scales exhibit a strongly convex 

 upper edge, which in the upper rows is still frequently drawn out in the middle into a 



