BRA CHIOP ODA. 
307 
of the shell, and in the cardinal area and articulating apophyses, and may 
be regarded as of some significance in determining the source and point of 
departure of the productoid stock. (Ehlert has demonstrated the existence 
of reniform or hook-shaped brachial ridges in the genus Stropheodonta (S. Le- 
blanci) ;* and although a feature of extremely rare occurrence in that group, 
it should be given full value in its bearing upon the same question. It has 
been remarked by many observers that in the earlier forms of Chonetes the 
reniform ridges are but faintly, if at all, manifest; the more distinctly pro¬ 
ductoid characters of the genus becoming pronounced only with the advent 
of Productus. f The peculiar cardinal tubes, which are continued into 
spines, sometimes of a length equal to that of the valves, constitute a feature 
found only in this group of shells, including Chonostrophia and Chonopectus, 
here described for the first time, Chonetina, Krotow, and Chonetella, 
Waagen. The existence of these passages across the ventral area, opening 
into the interior of the shell, was first observed by Keyserling,| and was dis¬ 
cussed at length in Volume IV of the Palaeontology of New York,§ and more 
recently by Mr. John Young, in Davidson’s Appendix to his Supplement on 
the Brachiopoda.il Fine hair-like spines are sparingly scattered over the striae 
in C. papilionacea, Phillips, of the Carboniferous limestone, and traces of similar 
processes have been mentioned by various writers for other speciesV 
It is probably true in many cases that the supposed bases of the spines are 
but the coarse punctations of the inner laminae of the shell-substance, exposed 
by the abrasion of the impunctate outer or epidermal layer. Furthermore, the 
Chonetes papilionacea is a species whose generic affinities are still debatable. 
The shell is of immense size, far exceeding that of any other form referred 
* Annales des Sciences Geologiques, vol. xix, p. 63. 
t (Ehlert observes “que les modifications du genre Chonetes ont lieu tout particuli&rement a l’epoque 
carbonif&re, et que leur tendance dans certaines especes, a de rapprocher de la forme producto’ide semble 
coincider avec l’apparition et la d6veloppement maximum du genre Productds. Les Chonetes d6voniens, et 
surtout ceux qui appartiennent a l’epoque silurienne, presentent des caracteres plus nettement d6finis et plus 
facilement reconnaissables.” 
| Geogn. Beobachtungen auf einer Reise in das Petschora-land, p. 213. 1846. 
§ “ “ ' “ “ P- 117- “ 
1 “ “ “ “ p. 281. 
If See Davidson, Carboniferous Brachiopoda, p. 188, pi. viii, fig. 8 b. 1872 ; Waagen, Salt-Range Fos¬ 
sils, genus Chonetes. 
