234 BRITISH CARBONIFEROUS BRACHIOPODA. 



20 of our work), and then cast a glance at another one of P. Yoimgianus (figs. 21 — 23), 

 a very great difference is observable between them, fig. 1 9 belonging, according to Mr. 

 Young, to another species. I am quite disposed to concur with Mr. Young, that in 

 the case of P. Youngianus the spines have nothing to do with the formation of the ribs, 

 but I am still uncertain whether in the fully grown or adult condition P. aculeatus was not 

 liable to become more or less ribbed towards its margin, for even in P. Youngianus, when 

 quite young, no ribs are discernible, but they become apparent with the growth of the 

 shell. 



Productus sub-lcevis (p. 177). Plate XXXI, figs. 1, 2; Plate XXXII, fig. 1; and 

 Plate LI, figs. 1, 2. 



This interesting species has been found by Mr. Wardle in the Carboniferous Limestone 

 of Caldon Low, Staffordshire. One specimen shows a row of spines projecting from 

 a median longitudinal ridge, which extends along the ventral valve, as represented in 

 PI. LI, fig. 2. The visceral portion of the shell is also sometimes very irregularly wrinkled, 

 although at other times it is comparatively smooth. 



Chonetes. 



I can add nothing to what has been stated in pages 179 — 191 of this Monograph. 

 There are, however, a few points which will require further consideration when more ample 

 material shall have been obtained. C.papilionacea has sometimes exceeded the dimensions 

 I have given ; for there exists in Sharp's collection at the Geological Society a specimen 

 from Kendal which measures six and a half inches in breadth by three in length. 



Crania and Discina (pp. 192 — 198). 



Nothing new has been found since my descriptions have been written. 



Lingula (pp. 199—210). 



ERRATA. 



At page 203, line 23, write — 1. Muscles Prkadducteurs (anterior adductor), &c. 



