BRA CHIOPODA. 
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. Meeeella 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 
pectiniformis, 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. pectiniformis, 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 
mentionedj; and S. 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. 
t Palaeontology of Eastern Nebraska, p. 170, pi. v, fig. 16. 
I Waagen has described this process in 8. pectiniformis as having precisely the same structure as that 
in 8. pelargonatus according to the figures given by Davidson. 
§ See Final Report U. S. Geological Survey of Nebraska, p. 177. 1872. 
