BRACHIOPODA. 205 



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

 radiating plumose strise. Shell-substance fibrous, punctate. 

 Type, Plicalula striatocostata, Cox. Upper Carboniferous. 



Observations. Meekella emljodies the extreme development attained by 

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

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

 cavity ; that in Hiri'ARiONTX 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 o£ Streptorhijnchus 

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

 acters of Meekella, and which was thus referred by Mr. Meek,! 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 Streptorhtnchus, such as that already 

 mentioned:}: and S. Halliunus, 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 Strepforhynchus 

 pelargonatiis. 



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. 

 t Palfeontology of Eastern Nebraska, p. 170, pi. v, fig-. 16. 



I WaaCtEN has described this process in 8. pectiiiiformis as having precisely the same structure as that 

 in (Sf. pelargonatiui according to the figures given by Davidson. 



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



