part 4] 



CAMBRIAN HORIZONS OF COMLEY, 



335 



the genera Mickwitzia and Kutorgina, to neither of which can 

 they be referred without an extension of one or other of the generic 

 diagnoses given by Dr. Walcott. 1 It is, therefore, necessary to 

 propose a new generic name, and it seems appropriate to dedicate 

 the genus to one who has done so much to aid the study of the 

 Cambrian faunas in general and the brachiopoda in particular. 



In common with the two above-named genera, Walcottina has 

 the ventral valve considerably elevated, while the dorsal, so far as 

 known, is comparatively flat ; the pedicle-opening is a gaping 

 orifice between the valves ; and the shell-substance is made up of 

 two or three principal layers. 



The characters in which the three genera are divergent, so far 

 as can be determined from the specimens of the new genus that 

 are available, are as follows : — 





Miclcwitzia. 



Walcottina. 



TLutorgina. 



(1) Shell-substance ... 



phosphatic. 



calcareo-eorneous. 



calcareous. 



(2) Exterior sculpture 



papillose. 



C concentric stri;e | 

 ( with flat bands. ) 



C concentric striae, 

 X imbricated. 



(3) Exterior surface of 

 interior layer 



( radiate and con- 7 

 | centric ridgelets. ) 



radiate corrugations. 



(, fine radiating lines 

 X and punctas. 



(4) Innermost surface 



punctate. 



smooth. 



? 



Ventral valve. 









(5) False area 



( obscurely deve- ) 

 I loped.' )' 



( not marked off from ~) 

 X remainder of shell. j 



( distinct, but short 

 ^ and rudimentary. 





No specimens of Walcottina have been found that are not more 

 or less in a decomposed condition, and consequently the exact 

 nature of the shell-substance cannot be ascertained. They occur in 

 a somewhat friable conglomerate from which all, or almost all, the 

 calcareous cement has been dissolved away, and with it, presum- 

 ably, any calcareous material that the shells may have contained. 

 The matter now representing the test, though soft, is often well 

 preserved, its surface-characters can be made out with certainty, 

 and the component layers are usually distinctly observable. The} r 

 have a corneous aspect, but may have been originally calcareo- 

 corneous. In this respect the specimens approach Miclcwitzia, 

 but the exterior sculpture and that of the interior layer are more 

 reminiscent of Kutorgina. 



The false area in Walcottina is non-existent, in Miclcwitzia it 

 ' may or may not be obscurely defined,' - in Kutorgina it is quite 

 distinct, judging by the figures given by Walcott. 3 In this respect 

 the proposed genus seems to be more primitive than the other 

 genera and to be on a par with Utistella. 4 * 



1 1912. pp. 329 & 579. 



- C. D. Walcott, 1912, p. 329. 



3 Ibid. pi. v, figs. 1 7; & 1 n. 



4 C. D. Walcott, op. supra cit. p. 327 & pi. i, figs. 1, 1 a-1 e. 



