186 



OOLITIC ECHINODERMATA. 



side in one of the buccal plates placed near the oral opening. No pedicellarige. Move- 

 ment (in the living state) effected by the rays. 



The Ophiuroidea range from the Silmian formation to the existing period, and are 

 represented in the British Liassic and Oolitic strata by one family (Ophiurid^), five genera 

 Ophioderma, Ophiolepis, Acroura, Amphiura, and Ophiurella), and twelve species ; 

 and are divisible into three sections (A, B, C), dependent upon the number of genital 

 fissm'es and the nature of disc. 



Family XIV.— OPHIURIDtE, Wright (Vol. II, p. 138). 



Body discoidal, depressed, having long slender rays ; disc covered with hard plates, 

 or membranous and naked. Two or four fissures {genital) in under side of disc in the 

 area bounded by the rays and margin of mouth {interbrachial space). Rays five, always 

 simple. Range from the Silurian to the existing period. 



Section A. — Four genital fissures in each interbrachial space. 



The section is represented in the British Liassic strata by one genus, Ophiodeema, 

 and five species. 



Genus 30. — Ophioderma, Mutter and Troschel (Vol. II, p. 140), 



Disc and arms smooth, covered with small closely set granules. Arms long and 

 slender ; lateral borders provided with short papillse or fine spines. Four genital fissures, 

 disposed in pairs in radial lines. Range of the genus from the Liassic to existing period. 

 Five British Liassic species (Vol. II, pp. 140 — 149). 



Section B. — Two genital fissures in each interbrachial space. Disc provided with plates. 



The section, ranging from the Trias to the existing period, is represented in the British 

 Oolitic strata by three genera (Ophiolepis, Acroura, and Amphiura) and five species. 



Genus 31. — Ophiolepis, Miiller and Troschel (Vol. II, p. 150). 



Disc provided with naked scales or shields on its upper surface. Two genital fissures 

 close to the arms. Oral opening bordered with a single row of hard papillae. Oral 

 plates simple and heart-shaped. Lateral borders of arms bearing papillae or spines. 



