CLASS ii ASTEROIDEA 205 



of the recent genera Ophiolepis, M. and T. ; Ophiocten, Liitk. (Fig. 331) ; Ophio- 

 f/l I//I/KI, ,'iinl (>i>lnoiinn<iiiiit, Lyman. Some of the forms described under the head 

 of Geocoma, d'Orb. (such as G. socialis, Heller, from the Callovien of La Voulte ; 

 or G. Libanotica, Konig, from the Cretaceous of Hakel, Lebanon), are incap- 

 able of precise determination ; others (such as G. carinata, Goldf., Fig. 332) 

 are closely related to the recent Amphiura. 



Ophiurella elegans, Agassiz, from the Lithographic Slates of Solenhofen, is 

 referred by Liitken to Ophiocoma, Agassiz. Other Jurassic and [Cretaceous 

 forms which have been described under various generic names are assigned 

 by the same author to Ophioglypha, Lyman. Fossil Ophiuroids which do not 

 admit of critical determination are usually grouped together under the general 

 term of Ophiurites. 



Class 2. ASTEROIDEA. Star-fishes. 1 



Asterozoans whose simple and more or less flattened arms are prolongations of 

 the central disk, and contain the hepatic appendages of the alimentary canal, as well 

 as the generative organs. Ambulacral feet disposed in rows along deep open 

 grooves on the under or actinal surface of the arms. 



Star-fishes have typically five arms (but in some cases as many as eight, 

 ten, twelve, twenty, or more), which are prolongations of the central disk, 

 and are not sharply marked off from the same. The integumentary skeleton 

 consists of plates which are either contiguous with one another along their 

 edges, or are united in a reticulate fashion, and covered with a leathery skin. 

 The calcareous plates often bear movable spines or bristles, or they may be 

 tuberculated or granulated. The abactinal surface usually exhibits a central 

 or subcentral anus, and also a madreporite, which is situated in one (rarely 

 two or more) of the interradii. The madreporite is covered with labyrinthic 

 furrows, and is perforated for the admission of water into the so-called stone 

 canal, whence it is conveyed into the water-vascular ring surrounding the 

 mouth. The fine pores and protrusive coecal processes (papulae), which in the 

 Phanerozonia are restricted to the dorsal surface, but in the Cryptozonia are 

 distributed over the whole body, serve as respiratory organs, the body fluids 

 being brought into close contact with the oxygenated water. 



The mouth occupies the centre of the dorsal surface, and is pentagonal in 

 contour, owing to the projection of five pairs of interradially disposed oral 



1 Literature: 

 Forbes, K, British Fossil Asteridae (Mem. Geol. Survey, vol. II., Part II., and Decade III.), 1848 



and 1850. 



Salter, J. IV., New Palaeozoic Star-Fishes (Ann. and Mag. Nat. Hist. XX.), 1857. 

 Gray, J. E., Synopsis of the Species of Star-Fish in the British Museum, 1866. 

 Simonowitsch, S., Ueber einige Asteroiden der rheinischen Grauwacke (Sitzuugsber. Wieu. Akad. 



LXIV.), 1871. 



Sars, G. 0., Researches on the Structure, etc., of the genus Brisinga. Christiana, 1875. 

 Perrier, E., Revision de la Collection des Stellerides du Museum d'Hist. Nat. de Paris (Arch, de 



Zool. Experim. IV., V.), 1875-76. 



Agassiz, A., North American Star-Fishes (Memoirs Museum Comp. Zoology, Cambridge, V.), 1877. 

 Viguier, C., Anatomic comparee du squelette des Stellerides (Arch, de Zool. Experim. VII.), 1878. 

 Sladen, W. P., Report on the Asteroidea (Scient. Results, Challenger Expedition, XXX.), 1889. 

 Sladen, W. P., Monograph on the British Fossil Echinodermata from the Cretaceous Formations, 



Vol. II. Asteroidea (Palaeontographical Society), 1890-93. 

 Fraas, ., Die Asterien des weissen Jura (Palaeontographica, XXXII.), 1886. 



