84 PALEONTOLOGY OF NEW YORK. 



The Devonian form, S. Maia, Hall ( ^ Athyris Maia, Billings), from the Cor- 

 niferous limestone, is an excellent representative of this type of structure both 

 externally and internally ; and the list is completed, so far as our knowledge 

 goes, by the addition of S. subumbona, Hall, of the Hamilton group. 



2. SepiaH. Shells in which dental plates or septa are well developed. 



We are compelled to recognize two groups of the septate Glabrati : 



(a) Martiniopsis, Waagen, 1883. Species with the lamellaB developed in 

 both valves. 



Waaokn has described two species of this genus, M. inflata and M. subpmtago- 

 nalis, from the Productus limestone of India,* and suggests that this type of 

 structure appeared in the Devonian. Beyond the account given by Dr. Waagen 

 we know nothing of these fossils. 



(b) ("Gen. nov.," Tschernyschew), Type of Marttnia semiplana, Waagen. 

 Shells with dental lamellae scarcely developed, but with a prominent median 

 septum in the pedicle-valve. 



Dr. Tschernyschew has called attention to the peculiar structure of this shell,f 

 suggesting the desirability of separating it from its usual association by a distinct 

 designation. The .species was embraced in the genus Martinia by Waagen, 

 who did not observe the presence of the internal septum. Waagen and 

 Tschernyschew call attention to the generic similarity of Kutorga's Spirifer 

 corculum with this species, both of which are from the Artinsk-beds, or Permo- 

 carboniferous of Russia. 



It seems very doubtful if these forms should be separated from Quenstedt's 

 genus Mentzelia X established upon the Spirifer medianics from the Muschelkalk 

 of Silesia (Tarnowitz) ; though Dr. Tschernyschew finds the essential differ- 

 ence in the presence of dental lamellae in the latter and their absence in the 

 Carboniferous species. Quenstedt compares these characters in S. medianiis to 

 those of S. glaber, saying that they " bios an der Wand ankleben, und sich nur 

 an der Spitze des Loches auf die zierliche dreieckige Querlamelle stiitzen." 



* Memoin Geological Survey of India ; Productus-limestone Fossils, p. 624. 



f Allgemeine ^olof^iscbe Kai-te von Russland, Blatt 139 ; Beschreibung des Central-Urals und Westab- 

 hanges, p. 369, pi. v, figs. 1, 3, 1889. 



{ Petrefactenkunde Deutschlands ; Bracbiopoden, p. 522, 1871. 



