OPIIIDSTKJMA. 



103 



LIST OF SPECIMENS, 



Catalogue 

 NuralMir. 



Oriciiml Number 

 Nuiubur. uf Spec. 



Locality. 



When 

 Collected. 



Whence obtaiocd. 



Nature of 

 Spc-eimen. 



195 I 

 196 



3/useuin of Comparative Zoiilof/y. 



12+ 

 4 



Mendocino, Cal. 

 San Francisco, Cal. 



Alex. Agassiz. 

 T G. Gary. 



Alcoholic. 



OPHIOSTIGMA LtJTKEN. 



Type of the Genus, 0. isacanthum Lyman. 



Disk granulated. Teeth. No tootli-papillre. Basal mouth-papilla3 

 very long, stout, and broad ; the others small and few, arranged so as 

 to cover the end as well as the sides of the angle of the mouth. Arm- 

 opines three, short, smooth, arranged along the sides of the side arm- 

 plates. Side mouth-shields large ; nearly, or quite, touching, so as to 

 form a ring round the mouth. Mouth-apparatus, as a whole, forming 

 a distinct, raised pentagon. Two genital shts, beginning outside the 

 mouth-shields. 



Ophiostigraa isacanthum Lymax. (Figs. 8, 9.) 



Ophlura hacantha Say. Joiirn. Phil. Acad., Y. p. 150. 1825. 

 Ophiosiigiua monUifonne Lutkex. Addlt. ad Hist. Oph., p. 132. 



Special Marks. — Upper arm-plates cleanly arched without; lower 

 arm-plates bounded within by an inner side and two inner laterals. 



Description of a Specimen. — Diameter of disk, o"""- ; from outer side 

 of mouth-shield to outer corner of opposite mouth-slit, 2.1'°'"- ; width 

 of arm without spines, .S""""- ; length of arm, 23.5'°'°- ; distance from 

 outer edge of mouth-shield to inner points of teeth, to that between 

 outer corners of mouth-slits, 1 : 1.2. Mouth-papilla?, four to six. Teeth 

 four, stout, short, squarish, with the cutting edge a little re-enteringly 

 curved. Mouth-shields broad heart-shaped, with a sharp peak within, 



