134 BULLETIN 82, UNITED STATES NATIONAL MUSEUM 



Hartlaub as variety planata, come from various localities between Santa Cruz and 

 Grenada, and there are also some without locality data. 



Intermediates occur between this variety and the typical form, as, for instance, 

 a 19-armed specimen from Blake station 249 which is very similar to the variety 

 planata but has the IBr series only partially "wall-sided" and the IIBr series almost 

 free with rounded sides. 



A further characteristic of the variety planata, according to Hartlaub, is that, 

 in contrast to the usual condition, the IBr series often have an excavated surface 

 whereby they appear somewhat wrinlded. But this feature also occurs in specimens 

 with the IBr series entirely free laterally; for instance, it is fairly well marked in the 

 types of pulchella. 



The IBr series, as well as the IIBr series, are commonly gently convex dorsally 

 and rise to a low synarthrial tubercle at the articulation. 



In the great majority of specimens in which the point can be determined the 

 radials are only partially visible. But in a 13-armed specimen from Blake station 

 277 the radials have the entire distal border free of the centrodorsal. 



In their essential features the IIBr series resemble the IBr series. They are 

 rarely in contact with their neighbors on the adjoining rays, but the two series on 

 a single ray are often in close contact with each other; at least, close contact between 

 the IIBri on a single IBr axillary is the rule. But as an exception there is a 17- 

 armed specimen from St. Lucia in which the IIBrj are wholly free interiorly. 



In the variety planata many of the IIBr series with the sides closely appressed 

 and flattened against their neighbors have a marked lateral thickening. 



Entire absence of IIBr series is rare. Hartlaub observed in all only 13 such 

 cases, including one specimen the specific identification of which is uncertain. Hart- 

 laub was at first of the opinion that the majority of the 10-armed specimens were 

 young, but he later came to the conclusion that this idea was not tenable, as among 

 the 10-armed examples he found specimens of all sizes. 



In 86 specimens with IIBr series in which the arm number can be made out, 

 the average number of the arms is 16.5. Twenty-one have 20 arms, 10 have 19, 

 and none over 20; not a single specimen possesses IIIBr series. 



The form of the arms, which above aU else determines the habitus of the indi- 

 viduals, is very variable and full of strong contrasts. Hartlaub remarks that greater 

 contrasts than those between the arms of the variety alata and those of the variety 

 planata with "wall-sided" division series are scarcely conceivable. In one direction 

 we find arms which are narrow at the base and gradually broaden toward the middle 

 and are composed of brachials which dorsally bear strong winglike processes, and 

 in the other direction we find entirely smooth and uniformly slender arms. Between 

 these two extremes there are all possible intermediates. There are also certain 

 other features of the brachials which vary between two wide extremes. 



Imbrication of the distal ends of the braohials is almost never, or only in rare 

 cases, present, and when it occurs it is only slightly developed. Correlated with 

 this is the usually smooth union of the ends of the brachials. 



Among very many specimens Hartlaub found only a single one (from Blake 

 station 158) in which there was a gradual, at first very slight, decrease in the width 



