EASTERN TROPICAL PACIFIC A8TER0IDEA. 107 



how many notable forms are recent discoveries, and emphasizes the fact that we 

 are as yet far from realizing the entire content of the family. This idea is still 

 further emphasized by the present collection, for while there are only eight disks 

 and some scattered arms from but five stations, no fewer than five species are 

 represented and foiu" of these are new to science.^ The one previously described 

 species moreover has liitherto been known only from the eastern tropical Atlantic, 

 where it was taken by the Challenger! Three of the five species were taken 

 at a single station. These facts all go to show how very incomplete our knowl- 

 edge of this remarkable deep-sea family still is. Of very few species has sufficient 

 material been secured to permit real knowledge of the specific characters, and 

 there is not a single form of which the growth-changes and the limits of indi- 

 vidual diversity are known. Under such circumstances the addition of new 

 species based on single and more or less fragmentary specimens is not very 

 desirable, but on the other hand material so rare and so difficult to secure must 

 not be ignored. The following notes may be of service in elucidating generic 

 and specific limits within the family. 



Brisingella monacantha,' sp. nov. 

 Plate 5, fig. 3, 4. 



Disk and number of rays unknown. Rays about 200 mm. long, 4 mm. 

 wide at base, 5.5 mm. wide at middle of genital area and 2.75 mm. wide one 

 hundred milUmeters from base. Genital area begins 10 mm. from proximal 

 end of ray and extends about 25 mm. ; it is covered by delicate naked gray skin 

 and is crossed by eleven or twelve calcareous ridges ("primary costae" of Fisher) ; 

 there are three or four additional costae distal to the swollen area and indications 

 of four or five more proximal to it ; there are two incomplete or secondary costae 

 on each ray; otherwise there is no calcareous material on dorsal side of rays. 

 Adambulacral plates about 2 mm. long on proximal half of ray, somewhat 

 shorter distally; width at proximal end about half length, distinctly less at 

 middle and shghtly more at distal end where there is a marked projection or 

 peak on the inner comer; at the base of this peak on the actinal surface of plate 

 but close to the adambulacral margin is a distinct spine-bearing tubercle; on 

 proximal part of arm, there is a fairly close approximation between costae and 



' It is interesting to note that all of the specimens were taken in water more than 2,200 fms. deep 

 and at a temperature lower than 36° F. 



2 monacanlhus = having a single thorn or spine, in reference to the armature of the adambulacral 

 plates. 



