AGASSIZ AND CLARK: REPORT ON ECHINI. 251 



PETALOSTICHA Haeckel. 

 CASSIDULIDAE Agass. 



ECHINONEIDAB Agass. 

 Micropetalon A. Ag. and Clark. 



This genus is related to Echinoneus, which it resembles quite closely superfi- 

 cially. It is at once distinguished from that genus by the fact that the poriferous 

 zones are flush with the test aud the pores extend only from the abactinal system 

 about half way to the ambitus. The anterior ambulacrum has about a dozen pairs 

 of pores in each zone; the zones of the lateral ambulacra have about 15 pairs 

 each ; and the zones of the posterior pair have about 20. The zones are very 

 narrow, close together at the abactinal system, diverge widely to below the am- 

 bitus and then converge somewhat to the actinostome. The primary tubercles 

 are few in number, not at all sunken into the test, and are arranged in regular 

 vertical series. Abactinally they have definite scrobicular circles of small second- 

 aries, but these are more or less imperfect actinally. Glassy tubercles are minute 

 and infrequent. Abactinal system as in Echinoneus. Genital openings four. 

 Actinostome very oblique. Anal system very large and oblique. Primary spines 

 rather long, nearly equal to width of anal system, slender and finely striated. 



Micropetalon purpureum A. Ag. and Clark. 



The single specimen collected is oval, flattened both above and beneath ; it is 

 17 mm. long, 15 mm. broad, and 8 mm. high. The actinostome is little sunken 

 and is 6 x 3 mm. The anal system is 6.75 x 3.75 mm. The genital openings are 

 conspicuous. On each side of each ambulacrum, close to the poriferous zone, is a 

 vertical series of about 14 primary tubercles, which extends nearly to the actino- 

 stome, but stops several millimeters from the abactinal system. Between these 

 two series, are two other series running from just above the ambitus nearly to the 

 actinostome, and in the posterior ambulacra there are two more rows between the 

 ambitus and the mouth. In each interambulacrum, there is a series of 14 or 15 

 tubercles on each side, extending from abactinal system to actinostome, and from 

 two to four others extend greater or less distances above and below the ambitus. 

 The color of the test is dirty-whitish above, becoming purple actinally ; the abac- 

 tinal system, poriferous zones, anal system, and actinostome are rich purple ; the 

 spines and tubercles are white. 



Station 3847. Off Lae-o Ka Laau Light, Molokai, 23-24 fathoms. 



