36 NATURAL, HISTORY BULLETIN. 



by Mr. Lyman, but when they stand on the dental plate they 

 should be considered as true tooth-papillae. The teeth are 

 stout, flattened, obtuse; they vary from three to eight in num- 

 ber. 



Dichotomous analytical table of the East Coast and West In- 

 dian species that have been referred to Ophiacantha, 

 [sens, ext.) 



[The species are grouped in this table as nearly in accordance with 

 their structural relations as possible. Those marked with an as- 

 terisk are from the eastern coast of the United States north of Cape 

 Hatteras. The others are from the West Indian region.] 



A. — Oral shields join the first side arm-plates. Adoral shields 

 entirely proximal to the oral shields. 



B. — True Ophiacantha. Disk wholly, and radial shields 

 mostly covered with small crotchets, thorny stumps, or 

 short spinules or granules, or with a mixture of these 

 forms. • 



C. — Disk covered with small crotchets, or short thorny 

 stumps, or short spinules, with no elongated spines nor 

 granules. 



d. — Arm-spines finely serrulated, or nearly smooth under a 

 simple lens, usually long and tapered, not glassy. 



e. — Basal opposite rows of arm-spines, in the adults, approxi- 

 mate dorsally. 



f — Mouth-papilla? form a simple row. 



* O. bidentata (Retz.) 



* O. aculeata Ver. 



* O. fraterna Ver. 



* O. abyssicola Sars. 



* O. anomala Sars. 



