160 Dr. G. J. Hinde on a 



and quite distinct from the vault-plates with which they con- 

 nect above, and they enclose and unite together the second 

 and third radials and the lower arrn-joints into one solid 

 immovable cup with the lower radials and basals. 



The vault is depressed, convex, and is formed of a peripheral 

 b order of numerous minute relatively thick plates, and a cen- 

 tral portion of larger plates covered with sinuous grooves and 

 tubercles. 



The column or stem is cylindrical, with alternately larger 

 and smaller joints. The rim of the larger joints is extended 

 into a sharp-edged flange. At irregular intervals there are 

 nodes, each bearing a whorl of five cirri. The central canal 

 of the stem is cylindrical and moderately large. 



The main differences between the characters assigned to 

 the genus by Prof. Williams and those above given consist 

 in the number and position of the interbrachial plates, the 

 absence of a series of smooth radiating plates in the vault, and 

 the nodal cirri of the stem. 



Prof. Williams does not directly mention interradial or 

 interbrachial plates, but states * merely that " along the 

 upper rim of the calyx is a row of small plates which lack the 

 tubercles," without further particulars as to their number, la 

 the fig. 1 of the plate accompanying his paper four of these 

 plates are shown in one interbrachial area, and but three in 

 another, and the plates of the vault apparently connect with 

 their upper margins. Nothing is stated or shown in the 

 figure of the plates above the anal plate. I am of course 

 unable to determine whether this notable difference in the 

 number of the interbrachial plates in H. Carpenteri and H. 

 ithacensis arises from the imperfect condition of preservation 

 of this latter species or is really existent ; but I should think 

 it probable that the vault-plates in Prof. Williams's speci- 

 mens have been pressed down over the higher zones of the 

 interbrachial plates, and thus concealed them from observa- 

 tion. 



With regard to the radiating rows of smooth plates in the 

 vault, which Prof. Williams observed in the cast of a single 

 crushed specimen of H. ithacensis, I am fairly confident that 

 there are no similar rows of plates in H. Carpenteri. The 

 apparently smooth character of the plates may arise from the 

 partial obliteration by wearing down of the tubercles, which 

 occurs in several of my specimens, so that they can only be 

 seen by careful observation with a lens, and the smooth plates 

 may therefore be really due to this cause. 



* Op. cit. p. >4. 



