292 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



Oral shields normal ; arms 4-6 times diameter of disc. 



Arms about 4 times diameter of disc; lower interbrachial space 



with less than 30 plates nivea. 



Arms about 6 times diameter of disc ; lower interbrachial space 



with more than 50 plates clypeata. 



Surface of disc lumpy and irregular, due to numerous, more or less 

 swollen, small plates. 

 Arms 3 or 4 times diameter of disc ; arm-spines nearly or quite equal 



to joint, rather stout impressa. 



Arms 4 or 5 times diameter of disc; arm-spines minute, about half as 



long as joint pacifica. 



Tentacle scale single, though the basal pores may have an extra small scale 

 on the inner side. 



Arm-spines 4 insularia. 



Arm-spines 2-3. 



First side arm-plates of adjacent arms meeting in interbrachial space dubia. 

 First side arm-plates not meeting. 



Arm-spines short and peg-like, not exceeding half the arm-joint. 

 Radial shields well separated. 



Most of the disc plates with one or more small but conspicuous 



tubercles projecta. 



Disc plates without tubercles or at most only a single large low 

 tubercle on some of the primary plates. 

 Upper arm-spine much the shorter; radial shield smaller than 



central primary plate stellata. 



Upper arm-spine the longer ; radial shield larger than central 



primary plate depressa. 



Radial shields more or less in contact, or rarely slightly separated. 

 Arm-spines 3 equal ; mouth shield wide, touching first side arm-plate 



on each side casta. 



Arm spines 2, lower longer ; mouth shield longer than wide, not in 



contact with first side arm-plate sincera. 



Arm-spines two-thirds as long as arm-joint or longer, radial shields 

 separated. 

 Side arm-plates meeting above, beyond first upper arm-plate 



antillarum. 

 Side arm-plates not meeting above, before third upper arm-plate at 

 least. 

 Side arm-plates entirely separate above, at least on basal half of 

 arm ; radial shields small, about as broad as long ; upper arm- 

 spine not longer than lower cont'igua. 



Side arm-plates meeting beyond third to eighth upper arm-plate; 

 radial shields large, longer than wide ; upper arm-spine the 

 longer. 

 Basal under arm-plates longer than wide ; arm-spine not exceeding 

 joint ; mouth shield scarcely pentagonal, lateral sides much 

 shorter than inner alba. 



