304 PROCEEDINGS OP THE GEOLOGICAL SOCIETY. [Jan. 4, 



88-91. Trochammina. We have elsewhere* expressed an opinion 

 that the Rotalia injtata of Montagu belongs to a subgenus distinct 

 from the common Botalice. The study of more varieties than we 

 were then acquainted with leads us to regard it as generically 

 distinct. The sandy structure, great variability of shape, and the 

 more or less imperfect formation of the chambers, are important 

 characters of this genus, which we have termed Trocliammina. 



The shell consists of a dense ferruginous cement filled with small 

 sand-grains which do not project above the surface. It resembles a 

 worked plaster- surf ace. It differs from the shell of Nubecularia, in 

 which the sand, when present, roughens the surface, but is often 

 absent ; and from that of Lituola where the sand is in greater pro- 

 portion than the cement, and is very coarse. 



The simplest forms of Trochammina belong to a species (T. irre- 

 gularis, D'Orb. sp.) of which we know three varieties. First, T. irre- 

 gularis proper (Webbinaf irregularis, D'Orb., Prodrome, ii. p. Ill ; 

 Bronn, Leth. Geog. 3rd edit. ii. pt. 5. p. 91, pi. 291. f. 27 ; " CEufs 

 des Mollusques," Cornuel, Mem. Soc. Geol. France, 2 ser, iii. p. 259, 

 pi. 4. f. 37+), which is adherent, moniliform, with more or less oval 

 chambers, and varying in the relative length of the stoloniferous 

 connecting tubes, in the number of the chambers, and in the 

 straightness or curvature of their line of growth. 



Secondly, T. irregularis altemans, which is adherent and has the 

 stolons springing from the chambers alternately and towards their 

 front, giving the shell a loose Textularian character. The chambers 

 are usually somewhat pyriform. 



Thirdly, T. irregularis clavata, which is another fixed form, and 

 consists frequently of a single pyriform chamber, tubular at one end, 

 and bearing a slightly margined and semioval aperture at the other. 

 The tubular portion frequently gives off another tube and chamber. 

 This bifurcation is also occasionally seen in T. irregularis (from the 

 Oxford clay) ; nor is it wanting in low forms of Nodosaria (Denta- 

 lina aculeata, D'Orb.). 



The second species, Trochammina squamata, comprises five varie- 

 ties, which are spiral, and more or less Rotalian, in their growth. 



The simpler of these forms, such as T. squamata incerta (Opercu- 

 lum incerta, D'Orb. For. Cuba, pi. 6. f. 16, 17; Spirillina arenacea, 

 Williamson, Monograph, p. 93, pi. 7. f. 203), consist of a long spiral 

 undivided chamber, having the shape of the clear, perforated, dis- 

 coidal Spirillina vivipara, Ehrenb., and of the white, opake, Milioline 

 Cornuspira foliacea, Philippi. 



T. squamata charoicles is a similar undivided tubular chamber ver- 

 tically spiral (instead of being complanate), and presents a curious 

 resemblance to the fruit of the Ghara. 



The third variety, T. squamata gorcUalis (from the Indian and 



* Annals Nat. Hist. 3 ser. iv. p. 347. 



t The name Wehbina was first applied by D'Orbigny to a few-chambered, 

 uniserial, curved form of Nubecularia (Webbina) rugosa, For. Canaries, pi. 1. 

 f. 16-18, and For. Foss. Vien. p. 74, pi. 21. f. 11-12. 



\ Fig. 36 is Lituola (Placopsilina) cenomana. 



