228 BULLETIN OF THE 



slits 3 mm. long and starting close to mouth-shields. Arm-spines three, 

 nearly of equal lengths, stout, rounded, blunt, and not tapering. Lengths 

 to that of under arm-plate, near disk, .8, .9, 1:1. Tentacle-scales two, flat, 

 nearly oval, and placed closely side by side. On outer side of tentacle-pore 

 is a semicircular rim or lip. Color, in alcohol, dull uniform purplish above. 



This speeies is of high interest as the first from the Pacific coast of North 

 America, which represents a genus peculiarly characteristic of the great 

 ocean. Oldoplocus imbricalus, described thirty years ago by Midler and 

 Troscht'l. has been brought in plenty from such diverse localities as Zanzi- 

 bar, Mauritius, New Caledonia, the Philippines, and the Kingsmill Islands. 

 It long remained the sole representative of a genus which was confined to 

 these faunal limits. 0. Exmurki differs from it in the precise way in which, 

 on the theory of Agassiz, species should differ within their genus, namely, 

 in the proportion of their parts. It will be therefore proper to briefly note 

 these differences. 0. oiihricatus is a thicker animal ; not only is the disk 

 thicker, but the arm is higher, having a width to height of 3..") : 3, from 

 which it follows that the arm-spines are less crowded, having more room ; 

 they also taper more, and the undermost is much the longest, having a 

 length of 1.3 : 1 as compared with the under arm-plate. The scaling of the 

 interbrachial space below is coarser and more uneven, having four or five 

 scales in the length of a mm., while in (>. Eamarki the smallest number is 

 five or six. The genital slit begins at some distance from the month-shield, 

 and is very short, while in 0. Esmarki it begins close to the mouth-shield, 

 and is longer. The minute lip or rim outside the tentacle-pore is barely to 

 be seen, while in the American species it is conspicuous. These differences 

 are all the more instructive from the fact that O. imbricatus is a singularly 

 steady species, and shows none of the variations offered by Ophiocoma sco- 

 hijti inlriiKi and 0. erinaci us in the same fauna. In examining great numbers 

 of individuals from many and distant localities, 1 have found no essential va- 

 riations in 0. imhriratiw, except three specimens from .Japan and one from 

 Java, in the Leyden Museum, in which the genital opening ran as far as the 

 mouth-shield. 



Professor Esmark found numerous specimens at San Diego, California, 

 among stones in shallow water. 



Amphiura (.1 mph i/>hnl!s) planispina v. Martens (Monatsbor. Kbnig. 

 Akad., Berlin, 180 7, p. 317). This species is originally described, perhaps 

 by a misprint, as having; only om mouth-papilla on each side, like Jlnniphn- 

 I/s. The originals, however, show three month-papilla? on each side. In 

 color if is just like OpJiinphmt/ivus Wurdemani, which, however, has a mar- 

 ginal fence of jointed scales round the disk, and its innermost mouth-papillae 

 are thickened, and run upwards towards the teeth. 



