BRACHIOPODA. 265 



marked with coarse costae, which, with the interspaces, are covered by fine 

 radiating plumose striae. Shell-substance fibrous, punctate. 

 Type, Plicatula striatocostata, Cox. Upper Carboniferous. 



Observations. Meekella embodies the extreme development attained by 

 certain features in the streptorhynchoid brachiopods. It has been noticed that 

 in Derbya the dental lamellae are septiform only in the apex of the umbonal 

 cavity ; that in Hipparionyx this character is more positive. In Meekella the 

 great development of these lamellae is subject to some variation, depending 

 primarily upon the depth of the umbonal chamber. Dr. Waagen remarks* that 

 in an American specimen labelled Meekella striatocostata, he was unable to discover 

 any trace of dental lamellae, and infers, from this fact, that there is probably 

 present, in our Upper Carboniferous fauna, a species of the type of Streptorhynchus 

 pec.tiniformis, Davidson, a form remarkable for having the peculiar exterior char- 

 acters of Meekella, and which was thus referred by Mr. MEEK,f who also 

 observed the absence of septa in the Indian species, S. pediniformis, and infer- 

 red a generic difference between it and Meekella in case this absence were not 

 accidental. 



The remarkable cardinal process in this genus is a feature of important 

 significance. In the pectenoid species of Streptorhynchus, such as that already 

 mentioned! ^^^ ^- Hallianus, Derby (see Plate XI, figs. 6-17), it does not 

 appear that there is a very close approach to Meekella in this respect, though 

 herein the Brazilian species is not in strict agreement with Streptorhynchus 

 pelargonatus. 



Meekella striatocostata is not an uncommon fossil in the Middle and Upper 

 Coal Measures of the interior and western States on the east side of the Rocky 

 Mountains ; but is not known in localities east of Illinois and Kentucky, " nor 

 anywhere in the Lower Coal Measures." § This species was described under 



* Salt-Range Fossils, Brachiopoda, p. 589. 

 + Palaeontology of Eastern Nebraska, p. 170, pi. v, fig. 16. 



I Waagen has described this process in S. peetinifoi-mis as having precisely the same structure as that 

 in S. pelargonatuf! according to the figures given by Davidson. 



§ See Final Report U. S. Geological Survey of Nebraska, p. 177. 1872. 



