216 HAWAIIAN AND OTHER PACIFIC ECHINI. 



proportionately large plates of the second series (PL 152, fig. 3). The peri- 

 stome is well forward, little sunken, and nearly twice as wide as long (PL 152, 

 fig. 3). The labrum is small, very low (or short) and wide. The color of test 

 and spines is pale yellowish gray. 



The primary spines are minute and slender anteriorly, but are longer ven- 

 trally and posteriorly; at the rear end of the test, they are three millimeters 

 long. The spines on the sternum are slightly spatulate at tip. Pedicellariae 

 are fairly common but are chiefly tridentate. A few triphyllous, with little 

 leaf-like valves, scarcely .08 mm. long, were found, and there was also one 

 rostrate seen. No globiferous or ophicephalous pedicellariae were detected. 

 The single rostrate seen had valves about .25 mm. long; it was not in any way 

 distinctive. The tridentate, on the other hand, are very characteristic. The 

 valves are .30-40 mm. long, with the blade strongly compressed at base, much 

 less so distally, the edges entire and smooth and the tip abruptly and strongly 

 hooked. 



It is probable that the specimens at hand of this species are all very young 

 and give no clue to the adult size, but the specimen figured shows all the specific 

 characters well. The shape of the test is markedly different from that of either 

 pyramidalis or hemiasteroides but is very much like that of micr aster oides. 

 The well-marked petals, however, distinguish placopetalus at once from the 

 West Indian species, to which, however, it is most nearly allied. 



Station 4146. Vicinity of Modu Manu, Hawaiian Islands. Bott. temp. 

 78.7°. 23-26 fms. Crs. co. s., for. 



Station 4160. Vicinity of Modu Manu, H. I. Bott. temp. 78°. 31-39 

 fms. Co., corln. 



Three specimens. 



Rhynobrissus micrasteroides. 



Rhinobrissus micrasteroides A. Agassiz, 1878. Bull. M. C. Z., 6, p. 192. 

 Plate 146, figs. 26, 27. 



The unique holotype of this species yielded just two pedicellariae. One 

 of these was a small tridentate with no distinctive features, but the other was 

 a globiferous pedicollaria of a very unusual and characteristic sort. The valves 

 (PL 146, fig. 26) are about .30 mm. long and markedly curved at the tip. which 

 consists of three long, slender teeth (PL 146, fig. 27). The stalk, which i- a 

 little longer than the valves has a conspicuous swelling near the base. This 



