220 HAWAIIAN AND OTHER PACIFIC ECHINI. 



brissus. I found no triphyllous pedicellariae on either of the specimens 

 examined. 



The Albatross collection contains half a dozen specimens, of which three 

 are from an unknown locality; the largest is a bare test 165 mm. long. There 

 is one small specimen from Laysan, H. I., and another only 9 mm. long from 

 near Modu Manu, H. I., 26 fms. In this last the generic characters are very 

 distinct but the specific characters are those of brissus. A slightly larger speci- 

 men 19 mm. long, from the Gulf of California, 7 fms. shows the beginning of 

 the dorsal keel in interambulacrum 5 but the posterior end of the test is still 

 vertical, as in brissus. 



Meoma. 



Gray, 1851. Ann. Mag. Nat. Hist., (2), 7, p. 132. 

 Type, Meoma grandis Gray, 1851, loc. cit. 



This characteristic, shallow- water, American genus contains but two 

 species, one in the West Indies, the other on the western coast of Mexico. The 

 differences between these two forms, except in color and in details of the pedi- 

 cellariae, are so slight and inconstant that I find even those mentioned by Mr. 

 Agassiz in the Revision to be quite unreliable. Globiferous and ophicephalous 

 pedicellariae are wanting in the genus, but the rostrate and tridentate are plenti- 

 ful and afford some specific characters. The subanal fasciole is very incomplete 

 and there is no real subanal plastron but whether this is a degenerate, a highly 

 specialized, or a primitive condition can only be determined when some of the 

 early growth-stages are known. 



Key to the Species of Meoma. 



Color deep blackish brown (little affected by preservation) grandis. 



Color reddish or yellowish brown, becoming dingy on drying vcntricosa. 



Meoma grandis. 



Gray, 1851. Ann. Mag. Nat. Hist., (2), 7, p. 132. 



This is the species of western Mexico, particularly in the region of the 

 Gulf of California. There are but two kinds of pedicellariae. The rostrate, 

 which are remarkably coarse and heavy, are similar to those of Brissus, but the 

 blades arc wide and the width is little or not at all increased at the tip: the valves 

 are strongly curved and measure .50-.80 nun. The tridentate are of two 



