DE ECHINIS. 193 



" De ECHINIS ET ECHINITIS, SIVE METHODICA EcHlNORUM DiSTRIBUTIONE, ScHEDIASMA 



JoANNis Philippi Breynii, M.D., ET SociET. Reg. Lond. Sodalis." 



" Genus I. — The Echinometra is an Echinus with the oral aperture placed in the centre 

 of the base, hut icith the anal one diametrically opposite at the summit. 



The term Echinometra occurs in Aristotle, who designates by it the largest genus of 

 Echini. Naturalists dispute whether, on this point, regard must be had to the size of 

 the spines, or of the test. Bellonius and his followers determine the latter. Hence I 

 think that this name is not inappropriately affixed to this Echinus, since those belonging 

 to this genus are found equal in size to an infant's head. There is this additional 

 peculiarity, that this genus, among all the Echini, is provided with very large spines and 

 tubercles. Its common name is Ovarius. 



The Echinometra has many peculiarities which distinguish it from other Echini, 

 besides the position of the apertures. 



1. Internally there are five testaceous teeth, each elaborately composed of several 

 parts, and surrounded by testaceous semicircles, which are situated internally around the 

 oral aperture. Some species of Echinanthus are also furnished with teeth, but of a 

 different structure. 



2. The test is divided into five equal or nearly equal areas. 



3. Externally it is rendered rough by tubercles, greater or smaller according to regular 

 series, placed for the purpose of receiving the sockets of the spines ; whilst in the other 

 Echini all the tubercles are nearly equal in size and very small. 



4. In like manner it has the primary and secondary spines more or less large and 

 unequal in size, whilst all the spines of other Echini are very small, and generally of 

 equal size. 



5. I have also especially observed near the anal aperture a small warty substance [the 

 madreporiform body], which can be more clearly distinguished with a lens, and similar to 

 that which Linck first detected in the Star-fish, the use of which in that animal will 

 doubtless throw light also upon this species of the Echinometra." 



[Plates V and VI of this work represent typical forms of this group.] 



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