BRACHIOPODA. 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. CEhlert 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 oJjserved by Keyserling,:}: and was dis- 

 cussed at length in Volume IV of the Palgeontology 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 strise 

 in C. papilionacea, Phillips, of the Carboniferous limestone, and traces of similar 

 processes have been mentioned by various writers for other species.TI 



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, ]>. 68. 



t CEhlbkt observes "que les modifications du g^enre Chonetes ont lieu tout particulifirement a Tepoque 

 carboniffere, at que leur tendance dans certaines especes, a de vappi'oclier (ie la forme producto'ide semble 

 coincide!' avec I'apparition et la d^veloppement maximum du genre Prodoctds. Les Chonetes d6voniens, et 

 sui-tout ceux qui appartiennent a I'epoque silurienne, presentent des caract^res plus nettement d6flnis et plus 

 facilement reconnaissables." 



X Geogn. Beobachtung-en auf einei' 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 ; Waaoen, Salt-Range Fos- 

 sils, genus Chonetes. 



