274 Dr. G. J. Hinde on Hystricrinus, Hinde^ versus 



punctobrachiatus appended to it, was privately circulated, but 

 never puhlished. Notwithstanding this, Prof. Hall made a 

 claim to the species ; and Prof. Williams, unwilling to dis- 

 oblige this veteran palseontologist, did not describe the form, 

 but only made the following remarks respecting it* : — 



" The arms, the shape of calyx, and the plates that were 

 preserved corresponded in general with the^. Itkacenst's, but 

 the tubercles on the calyx plates are finer, more numerous, and 

 the pitting very indistinct, and the basal plates are relatively 

 larger than in the typical specimens of that species. Hence 

 we are led to believe that the Hamilton species is distinct from 

 the Chemung specimens, ajid even if it were 'pro'perlij de- 

 scribed and puhlished, it is probably safe to regard it as a 

 distinct species. Although the specimen shows no trace of 

 the free sj)ines'[, the nature of the tubercles leaves little doubt 

 of a generic identity with Arthroacantha Ithacensis, and the 

 Hamilton form maybe called Arthroacantha jninctohrachiatay 

 Again, on p. 86 : — " This species [i. e. A. ithacensis'] differs 

 from the A7'th. punctohrachiata of the Hamilton group in the 

 more distinct and less numerous tubercles on the surface of 

 the calyx plates ; the smaller size of the tubercles leads to the 

 inference that the spines were smaller in the Hamilton form ; 

 the calyx plates were apparently thicker in the Chemung 

 Bpecies, and the second and third plates of the specimen of 

 Arth. punctohrachiata are higher than i\\o?>QoiArth. Ithacensis.''^ 



One needs hardly ask the question seriously, whether the 

 above general remarks and inferences, mostly of a negative 

 character, can be regarded as sufficient to define a species. 

 Under the twelfth rule of the British Association it is stated, 

 " two things are necessary before a zoological term can 

 acquire any authority, viz, definition and publication. Defi- 

 nition properly implies a distinct exposition of essential 

 characters, and in all cases we conceive this to be indis- 

 pensable." There is evidently no distinct exposition of the 

 essential characters of a species to be obtained from the cursory 

 observations of Prof. Williams respecting Hall's MS. speci- 

 men ; and it is clear that if this author had intended to have 

 described P. p)unctohrachiatus, Hall, MS., he would have 

 furnished all the particulars of form, the exact measurements, 

 and the figures, in the same manner as in the species A. 

 ithacensis J Avhich he professed to describe, and did so in a very 

 able and satisfactory manner, notwithstanding that his speci- 

 men was only a negative cast of the form. 



I maintain therefore that Messrs. Wachsmuth and Springer 

 are certainly in error in asserting that P. punctobrachiatus is a 

 good species and must be credited to Williams. It seems to 

 * Ihid. p. 83. t The italics are mine. 



