284 Raymond — Common Devonian Brachiopods. 



Pholidostrophia iowaensis Owen. 

 Pal. N. Y., iv, 1867, p. 104, pi. 18, fig. 1. 



Changes during Development. — This shell, like the other 

 Stropheodontas, becomes strongly alate in the neanic stages, 

 but the principal change during its development takes place in 

 the adult and early senile stages, when the shell which has 

 formerly been nearly flat is abruptly deflected in front, mak- 

 ing the ventral valve very convex in this part, while the dorsal 

 is correspondingly concave. The exterior is smooth in all 

 stages. A single specimen from Eighteen Mile Creek shows a 

 few distant radiating striae, which may be taken as suggestive 

 of an ancestral character. 



Brachial Markings. — In front of the 

 muscle scars of the brachial valve, there 

 is, on each side of the strong median 

 septum, a crescent-shaped ridge, which 

 turns in rather abruptly as a sort of 

 hook at the anterior end (figure 2). In 



Figure 2. — Pholidostro- n-i-.ii ±. j i, , > 



phia iowaensis Owen; adults these processes extend about two- 

 brachial valves, showing thirds the distance to the front of the 

 muscle scars and brachial shell. In the young, they extend some- 

 ridges. Natural size. what further Ward ^ and are more 



divergent. These ridges correspond, in position, with the 

 brachial ridges of Chonetes and Productus and probably 

 should be correlated with those markings. They have been 

 given considerable taxonomic importance by some authors, 

 the group of Stropheodontas which bears them being con- 

 sidered by (Ehlert as forming a transition group connect- 

 ing the Strophomenidse and the Productidse. It is prob- 

 able, however, that the occurrence of these markings is due 

 more to the age of the individual shell than to anything else, 

 for with increase in the deposit of testaceous matter the bra- 

 chial scars become more distinct in those species in which they 

 are usually observed, and these scars are not confined to the 

 Devonian Stropheodontas but can be seen in Pafinesquina 

 from as old a formation as the Chazy ; they are likewise well 

 known to occur in R. Jiikesii and Stropheodonta profunda* 

 The genus Pholidostrophia was suggested by Hall and 

 Clarke to include a section of the Stropheodontas in which the 

 shells were concavo-convex, had no striae, and were strongly 

 punctate. The interior of the dorsal valve was characterized 

 by having three divergent ridges in front of the muscular 

 area. Stropheodonta nacrea Hall, from the Corniferous and 

 Hamilton, an unnamed species from the Corniferous, axidStro- 



*See Hall and Clarke, vol. viii, pt. i, pp. 282, 283, figs. 19, 20 ; and pi. 20, 

 fig. 30. 



