128 ON AN ABNOEMAL AMBLYPNETJSTES. 



tively early period in its life-history the specimen of Ambly- 

 pneustes now under description met with some powerful external 

 influence, which affected the development of one of its five arese ; 

 the plates that had been formed were, with the growing down of 

 the neighbouring plates towards the actinostome, gradually forced 

 down and off. At the period of its capture some three pairs of 

 complete plates remained to give an indication of its experiences ; 

 had its capture been a little delayed, the plates of the fifth 

 segment or area might have been completely forced off; and a 

 specimen which would perhaps have been unique among recent 

 forms w r ould have been collected by the officers of H.M.S. ' Chal- 

 lenger.' What has been prevented here may, however, some day 

 happen. One such test has already been preserved as a fossil. 

 This, fortunately for the credit of science, came into the hands of 

 Hermann von Meyer, who, far from elevating it into a new genus, 

 put on record his belief that it was not even sjoecifically separable 

 from the Cidarites coronatus * of Goldfuss. Von Meyer's spe- 

 cimen does not appear to have presented any indications of 

 injury. The chief object of the present communication is to make 

 any other course than such as this extremely difficult. The zoo- 

 logist who proposes to differentiate a quadriradiate species, on 

 the ground of the absence of one area, will first have to show that 

 the specimens in his hands have not suffered from some accident. 



With more or less reason, some naturalists have looked on the 

 possession of other than five rays as a character of some specific 

 value among the Asterida and Ophiurida, and have considered 

 that, on account of its greater rarity among the latter, it is of 

 greater value as a mark of distinction. There is much to be said 

 for this view, but it must not be carried too far ; and even with- 

 out the restrictive influence of Dr. Philippi's abnormal Echinus 

 melo and this A. formosus, a naturalist would be hardy indeed 

 who w^ould ascribe to a difference in the number of rays of a 

 regular Echinid any other value than that which is justly due to 

 an interesting accident. 



Dr. Philippi, indeed, concludes his notice of his monstrous 

 form by saying, " Ueberhaupt scheint bei den regelmassigen 

 Echiniden die Natur nicht selten wenig auf die Symmetric der 

 einmal vorkommenden Organe zu geben ; " and he instances the 

 four anal plates of Echinocidaris and the strange elongation of 

 Echinometra. As to the former case, on which I will now only 



* Nova Acta Leop.-Car. Acad, xviii. i. (1836) p. 287. 



