768 



THE VOYAGE OF H.M.S. CHALLENGER. 



less compressed from both jjoles of the shameless axis, lenticular or discoidal, sometimes 

 square. It is enveloped by a voluminous calymma constantly bearing coronals of 

 " Myophrisca " {comjaare p. 724). 



Synojjsis of the Genera of Quadrilonchida. 



I. Subfamily 



Acanthostaurida. 

 All twenty spines simple, 

 without lateral apophyses 

 (sometimes forked, but 

 neither branched nor 

 latticed). 



II. Subfamily 



Litbopterida. 



Either all twenty spines or 

 a part uf them provided 

 with two opposite lateral 

 branches or apophyses. 



Four equatorial spines of 

 equal size and form. 



' Eight tropical and eight 

 polar spines nearly 

 equal, . 



Eight tropical and eight 

 polar spines very 

 diiferent, 



f Two principal spines of 

 Four equatorial spines of | equal size and form. 



very different size or J 

 form (the two lateral 

 constantly equal). 



Two principal spines 

 (frontal and caudal) 

 ver)' different, . 



Apophyses simple, neither branched nor latticed, 



}■ Apophyses branched or pinnate, but not latticed, 



Apophyses latticed, with fenestrated network, . 



334. Aranfhostaiinis. 



335. Belonostaurus. 



336. Lonchostaurus. 



337. Zijostaurus. 



338. Quadrilonche. 



339. Xiphoptera. 



340. Lithopitera. 



Subfamily 1. Acanthostaurida, Haeckel, 1881, Prodromus, p. 466. 

 Definition. — Q u a d r i 1 o n c h i d a with simple radial spines, without apophyses. 



Genus 334. Acanthostaurus,^ Haeckel, 1862, Monogr. d. EadioL, p. 395. 



Definition. — Q u ad r i 1 o n c h i d a with four equatorial spines of equal size and 

 form, which are much larger than the sixteen other spines. Eight tropical and eight 

 polar spines nearly equal. No apophyses. 



The genus Acanthostaurus is the most simple and primitive form of the Quadri- 

 lonchida, and the common ancestral genus of this family ; it is at the same time its most 

 common and widely distributed form. Some species apjjear in astonishing numbers in 

 different seas. It has been derived from Acanthometron by stronger development of 

 the four equatorial spines, which are all of equal size and much larger than the sixteen 

 others. 



' Acanthostaurus = &]>me-CTO!iS ; oix-afSa, ctcivoo;. 



