Nomenclature of the Foraminifera. 467 



of Peneroplis (scarcely two alike) are to be found in the Grignon 

 Tertiary deposits, and also, at the present day, in the deeper 

 waters of warm latitudes. The broad nautiloid Peneroplides 

 indicate shallow water. 



Some of the Grignon deposits appear to have been formed in 

 shallow water ; other beds are such as may be met with in the 

 Red Sea, at from 300 to 500 fathoms. Those beds, however, 

 that are rich in large specimens of Foraminifera have their 

 parallel very exactly in the deposits of the coral-lagoons and reef- 

 margins of the Australian Seas. 



21. Spirolinites cylindracea, /3. Ann. Mus. v. p. 245 ; viii. 

 pi. 62. f. 16 a, b. ; Tabl. Enc. Meth. pi. 466. tSa,b; Hist. An. 

 s. Vert. vii. p. 603. " Fossil; Grignon." 



This has no relationship with the foregoing. It is a variety 

 of another and very distinct species, and is of extreme interest 

 among Foraminifers, being, as it were, an uncoiled and almost 

 uniserial, dimorphous form of Valvulina triangularis, D^Orb. 

 The typical form of V. triangularis is a triserial, three-sided, 

 pyramidal shell, taking three cells to make a turn of its spire, 

 and having its aperture furnished with a peculiar tongue-like 

 flap or valve, as seen in D'Orbigny's Model No. 25. 



Valvulina has a sandy shell. Many Foraminifers figured and 

 described by authors as Valvulin(B are Rotalia. Some of the 

 regular forms of V. triangularis closely resemble Verneuilina 

 tricarinata (a subspecific form of Textularia agglidinans). 



When the trifacial compression of the shell becomes obsolete, 

 a close approach is made to Textularia Trochus, which, however, 

 has but two cells in one turn of the spire. A small specimen 

 of this variety is figured by us in the Ann. Nat. Hist. 2 ser. xix. 

 pi. 11. f. 15, 16. This trochoid form of Valvulina is sometimes 

 extremely depressed, and becomes scale-like and flat, resembling 

 some RotalicE, Williamson has described and figured such a 

 form under the name of Rotalina fusca, Monogr. p. 55, pi. 5. 

 f. 114, 115. 



Other varieties, on the contrary, widely differ in shape, the 

 triangular portion being obsolete, and the several chambers of 

 which the shell is composed, failing to make one coil of the 

 spire, form an obliquely scmioval shell, having a broad, flat, 

 oblique septal plane, with a large valve. This valve, sending 

 processes of shell-matter over the great crescentic aperture, 

 converts the usually simple passage into a semilunar series of 

 subquadrate passages. Here we have an isomorph of Bulimina 

 variabilis, D^Orb. Our specimens are undescribed, and come 

 from the Norwich Chalk and the Grignon Tertiary ; some also 

 occur recent in Australia. 



V. triangularis has sometimes a tendency in its later cham- 



31* 



