294 Dr. P. II . Carpenter on the 



with the hydrospiric sac through the poral openings. I do 

 not deny that this may have been the case in Pentremites and 

 its allies, which had marginal pores to the ambulacra ; though 

 I need scarcely say that I do not believe it to have been so. 

 But I should like to ask Mr. Ham bach one question. He 

 has stated *, and in my opinion quite rightly, that " the 

 condition of life was undoubtedly a similar one throughout 

 the whole class, therefore it cannot very well be called an 

 arbitrary assumption to suppose the presence of certain organs 

 with the same physiological functions in all these animals." 

 Hence if the sides of the ambulacra of Pentremites were 

 fringed with tentacles communicating through the marginal 

 pores with the hydrospiric sacs, similar tentacles must also have 

 been present in Orophocrinas, Pkcenoschisma, Reteroschisma f 

 and Codaster ; but where were the pores through which they 

 could have been protruded ? 



Romerf pointed out long ago that the ambulacra of 

 Codaster were not provided with marginal pores ; and his 

 statements" have been confirmed by Rofe |, Billings §, and by 

 Mr. Etheridge and myself ||. In this genus, too, the hydro- 

 spires open directly upon the external surface of the body 

 between the ambulacra, their number varying from six to ten 

 on each side. Will Mr. Hambach tell us how the communi- 

 cation was effected between the tentacles of Codaster and the 

 hydrospiric sacs'? The same difficulty presents itself in the 

 case of Pkcenoschisma and Orophocrinus. 



The absence of pores in 0. inflatus and 0. Waterhousianus 

 was noticed by Rofe ^f ; while Meek and Worthen ** men- 

 tioned the same peculiarity in 0. stelliformis. Mr. Etheridge 

 and myself have alluded to itas acharacter of Pkcenoschisma tt> 

 and Wachsmuth has done the same for Heterosckisma \\. The 

 hydrospires of all these types, however, must have had ten- 

 tacles in connexion with them, if Mr. Hambach is right in 

 his restoration of the ambulacra of Pentremites. 



He makes great use of these supposed tentacles of Pentre- 

 mites in trying to establish the close relationship of this genus 

 with the Echinoidea ; but he entirely fails to see that if he is 

 correct in regarding the tentacles of Pentremites as commu- 

 nicating with the hydrospiric sacs which terminate in the 



* Trans. St. Louis Acad. vol. iv. p. -547. f Op. tit. p. 62. 



\ "Notes on some Echinodermata from the Mountain Limestone," 

 Geol. Mag. vol. ii. 1865, p. 250. 



§ ' Annals,' ser. 4, vol. v. p. 263. || Ibid. ser. 5, vol. ix. p. 232. 

 % Loc. tit. p. 250. ** ' Palaeontology of Illinois,' vol. v. p. 463. 



tt ' Annals,' ser. 5, vol. ix. p. 227. 

 Jt ' Palaeontology of Illinois,' vol. vii. p. 356. 



