MILIOLIDA. 



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Genus — Peneroplis, De Monffort. 



Nautilus, ForsMl, Spengler, Linni, Gmelin, Batsch, Fichtel and Moll. 



Spirolina and Cristellaria, Lamarck. 



Peneroplis, De Montfort, De Blainville, D'Orbigny, Carpenter, &c. 



General characters. — Shell free, equilateral, regular, more or less nautiloid. Form 

 very variable; lenticular, outspread, or crozicr-shaped. Surfaee usually obliquely striated. 

 Each convolution formed of numerous narrow undivided segments. The outer whorl 

 embracing those within it, and in the complanate varieties almost concealing them. 

 Apertures variable, either single (in young shells) or numerous and distinct, or else 

 taking the form of one large dendritic orifice caused by the coalescing of a hnear series 

 of pores. 



Suhgenus — Dendritina, U Orhigny. 



General characters. — Shell nautiloid, lenticular, turgid. Pseudopodial aperture large, 

 irregular, dendritic. 



1. Dendritina ARBUSCULA, 2)' Orizy«y. Plate III, figs. 48, 49. 



Dendritina ARBUscuLA, D"0r6., 1826. Module No. 21. Ann. de Sc. Nat., vol. vii, p. 2S5, 



No. 1, pi. 15, figs. 6, 7. 

 Peneroplis planatus (F. and A/.), var.. Carpenter, 1859. Phil. Trans., vol. cxlix, p. 9, 



pi. 2 ; Introd. For., p. 88, pi. 8. 



Characters. — Shell nautiloid, turgid, thickened at the umbilicus, rounded more or less 

 at the margin. Aperture a single large ramifying orifice, formed by the coalescence of 

 numerous small pores, arranged either in a line or otherwise. Diameter, .'^th inch. 



In speaking of the earlier authors who have studied the different forms of Peneroplis 

 ('Ann. Nat. Hist.,' March, 1865), we have stated om- views fully fis to the value of the 

 subdivision of the type into genera and species. (See also Carpenter's memoir, ' Phil. 

 Trans.,' 1859, and his 'Introd. Foram.,' p. 84.) Notwithstanding the wide variations in 

 general contour, and in the nature of the pseudopodial apertures which may be observed 

 in different specimens, there can be no doubt that the whole constitute but one true 

 species. At the same time we are able to divide them roughly, according to the nature 

 of their divergence from the central type, into three or four groups, for which, as causing 

 least confusion, we propose to keep the well-known and hitherto accepted names, giving 

 to them a subgeneric place. Of these groups, that centering in Peneroplis {Dendritina) 



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