MONOGRAPH OF THE ECH1NODERMATA. 501 



of Lamarck's divisions, and in 1839 Agassiz proposed to se- 

 parate the Echini into three natural families — Spatangi, Cly- 

 peastres, and Cidarites. 



1. Spatangi. 



Disaster. Holaster. Ananchytes. Hemipneustes. Micraster. Spatan- 

 gus. Amphidetus. Brissus. Schizaster. 



2. Clypeastres. 



Catopygus. Pygaster. Galerites. Discoidea. Clypeus. Nucleolites. 

 Cassidulus. Fibularia. Echinoneus. Echinolampas. Clypeaster. Echi- 

 narachnius. Scutella. 



3. Cidarites. 



Cidaris. Diadema. Astropyga. Salenia. Echinometra. Arbacia. 

 Echinus. 



With more immediate reference to the part before us, Mr. 

 Gray, in the Zoological Proceedings of 1835, has suggested 

 a subdivision of the genus Echinus into what he considers 

 four natural genera, viz., — Arbacia, Salenia, Echinus, and 

 Echinometra, from a belief that some of the characters on 

 which the genus had been founded, such as the number of 

 the tesserae and the pores in the ambulacra, were discovered 

 to be inconstant. 



The genus Salenia, as originally established by Mr. Gray, 

 was characterized by having the ambulacral arese narrower 

 than the interambulacral ; by having only one large imperfo- 

 rate tubercle upon each coronal plate, and of which the ova- 

 rial and the interovarial plates (united together so that they 

 cannot be easily separated) form a salient disk, traversed by 

 the anal apparatus [appareil), of which the opening is some- 

 times central, sometimes anterior, and sometimes posterior. 

 Agassiz, however, finding differences in the oviductal appa- 

 ratus, has been induced to raise the genus Salenia into a fa- 

 mily consisting of four genera, according to the modifications 

 presented by this apparatus ; viz., Salenia, properly so called, 

 Goniopygus, Peltasies, and Goniophorus. No recent species 

 are known, and the fossil ones are entirely confined to the 

 cretaceous series. 



Salenia, Gray, Agas. 



Having a single plate placed in the middle of the oviduc- 

 tal apparatus, called the superanal plate, and which, accord- 

 ing to its position opposite to the anal opening, renders the 

 anus always eccentric, sometimes throwing it in front and 

 sometimes behind. This superanal plate is generally of the 

 same size as the ovarial plates, and forms with them, as well 

 as with the five interovarial plates, a circular disk, variously 

 notched in its contour. 



