19 



across the margin. The calyx walls are covered with numerous small scales transversely disposed, 

 but in numerous rows both vertical and transverse. These scales are very short and broad with 

 their upper e.xposed edges finely ctenate and apparently overlapping the base of the next scale 

 above. The number of scales in a horizontal row is hard to determine owino- to their small 

 size, but there seems to be as many as 20 or more in each row. The tentacles are covered 

 with similar rows of narrow scales fitting the dorsal surface and looking like continuations of 

 the rows on the calyx walls. 



Spicules. These are narrow scales with curved and ctenate borders. On the basal 

 parts of the calyces and in the coenenchyma of the stem and branches they become so narrow 

 as to assume the form of spindless with tuberculate or echinulate surfaces. 



Color. The color is almost pure white, in alcohol. 



Peltastisis new genus. 



{ttsXtxo-t-^: and /y;-:). 



Colony unbranched; polyps uniserial and provided with true opercula consisting of eight 

 parts or flaps, each part consisting of a single triangular scale; calyces with spicules of the 

 primnoid type, being flattened scales with irregular branched or ctenate edges and with thorny 

 points on the surface. 



The type of this genus is Peltastisis uniserialis Nutting. The only other known species, 

 also found in the Siboga collection, is described beyond. 



These two species undoubtedly belong to the family Isidce^ and can, without violence, be 

 admitted into the subfamily Mopseince. They are so different, however, from any previously known 

 members of this group that it becomes necessary to construct a new genus for their reception. 



The genus Peltastisis bridges the narrow gulf between the Isida and Primnoidec in one 

 important particular in that it combines the jointed axis of the former and the characteristic 

 operculum of the latter, which it also resembles closely in its spiculation. Indeed, it is .so 

 directly intermediate between the two families that it can only arbitrarily be placed in either. 

 The character of the axis is, however, of sufficient importance in the opinion of the writer to 

 determine the position of Peltastisis as a member of the family Isidcc. 



I. Peltastisis imiserialis new species. (Plate IV, figs. 3, 3a; Plate VI, fig. 3). 



Stat. 145. 0°54' S., 1 28° 39.9 E. 827 meters. Hard. Pumice stone. 

 Stat. 159. o°59'.iS., I29°48'.8E. 411 meters. Coarse sand. 



Colony consisting of a very delicate unbranched stem growing from a calcareous, lobulated 

 flattened base and attaining a length of 6.2 cm. The basal i.i cm. of the stem is devoid of 

 polyps. The basal internode measures 2 mm., the second 2.9 mm., the third and succeeding 

 ones about 3 mm. The horny nodes are very short, about .5 mm., and much narrower than the 

 calcareous ones. The polyps are uniserial and about 1.7 mm. apart, from summit to summit. 



The individual calyces are club-shaped or conical, i mm. in height on their abaxial side, 

 inclined toward the branch so that the adaxial side is almost contiguous with it. The margin 



