28 



PALEONTOLOGY OF NEW YORK. 



termined, but we have evidence that the outer or epidermal layer is more 

 largely corneous than those within, and, so far at least, its structure is in 

 harmony with that of Lingula, as demonstrated by Gratiolet. But on the 

 other hand, the relative amount of mineral matter in the shell is far in excess 

 of that in Lingula, and its structure in this respect is wholly in consonance with 

 the other features which establish its transitional position in the line of de- 

 velopment from Lingula to Trimerella. In the latter genus and its associates, 

 the heavy shells have been rarely preserved, or when preserved, their original 

 structure is so essentially altered by dolomitization and crystallization, that it is 

 impossible to gain an accurate conception of their composition. Undoubtedly 

 they were substantially calcareous, with small percentages of organic matter, the 

 latterperhaps relatively increased in the thinner-shelledforms,likeD[NOBOLUSand 

 some species of Monomerella. The evidence at hand would lead to the presump- 

 tion that the loss of the organic constituents of the shell, and the increase 

 in calcareous matter, progressed pari passu with the assumption of Trimerelloid 

 characters: 



Genus LAKHMINA, GEhlert* 1887. 



1885. Davidso7ieUa,\VAAaEH. Mem. GeoL Surv. India ; Palaeoiitologia Imlica, Sei-.XIII, I.iv, fasc.y, p.762. 



Not Davidsonena, Muniee-Chalmas, 1880. Bull. Societe Gtologique de France. 

 1887. Lakhmina, CEhlert. Fischer's Manuel de Conchyliologie ; Brachiopodes, p. 12G5. 



This genus is defined by Dr. Waagen in essentially the following terms: 

 General outline more or less linguloid. 

 The ventral valve is the larger and 

 possesses a prominent apex, which is 

 provided, on its lower surface, with a 

 deep furrow for the pedicle. Li the in- 

 terior of the ventral valve, the cardinal 

 margin is somewhat thickened, without 

 forming a distinct area. Below this 



Davidsonella [=LaJ:hmina) linguloides, after Waagen. 

 Fig. 13. Pecliclevalve. Fig. U. Brachial T.nlve. 



* In the preparation of the discussion of this genus, and g-ei^erally throug-hout the volume, the term 

 Davidsokblla had been adopted, not being- aware that the name had been used by Mukibr-Chalmas in ISSO 

 for a genus of Liassic brachiopods allied to Thecididm. We are therefm-e reluctantly compelled to adopt the 

 term Lakhmina, jiroposed by CEhlbrt; though it must not be forgotten that it is to Dr. Waagen we are 

 indebted for the careful aiialy.sis of the genus. 



