846 



SYSTEMATIC HISTORY OF THE INFUSOEIA. 



marginal ones; indeed sometimes tliey 

 are very indistinct. 



A. Americanus (E.). — Disc with 

 strongly marked lines, radiating inwards 

 from the margin and leaving an irregidar 

 central space destitute of lines. EM. 

 pi. 33. 14. f. 2. United States. The 

 large processes, as well as the central 

 space, are without the radiating lines of 

 A. scidptus ; but we think it probable 

 that Ehrenberg's figm'e was taken from 

 a specimen of that species in which 

 those markings were more than usually 

 inconspicuous. 



A. cylindricus (E.). — Frustules cylin- 

 drical, with a plane orbicular disc on 

 each side, having a rim and a central 

 area marked by various radiating lines ; 

 processes resembling oblique openings. 



A. oralis (Arnott, MS.). — Disc oval, 

 with two opposite, narrow, hispid ele- 

 vations midway between the roundish 

 perforation-like apices of the processes ; 

 curved lines punctate, rather faint ; um- 

 bilicus obsolete. Algoa Bay and Peru- 



vian gnanos. Communicated by Mr. 

 Kittoni This species is distinguished 

 by its oval disc and hispid elevations. 

 The truncated processes do not in general 

 correspond exactly with the longer dia- 

 meter of the valve, but are placed a little 

 on one side in opposite directions, in 

 which respect, as well as in the presence 

 of hair-like spines, it approaches Cera- 

 taulus. 



Doubtful Species. 



A. polystigmus (E.). — Radiating series 

 of cellules converging in two lateral 

 obsolete whorls, which appear perforated 

 (processes ?). CelMes 14 in 1-1200". 

 Diam. 1-360".= Coscinodiscus poly stigma. 

 KA. p.l24. North Sea. 



A. ? gigas (E.). — Margin of sides tu- 

 mid, looking as if perforated, sculptured 

 bv elegant rows of dotted, imperfectly 

 radiairt lines. EM. pi. 19. f. 63. = Cos- 

 cinodiscus Auliscus, KA. p. 126. Fossil, 

 ^gina. Ehrenberg's figm'e represents 

 a mere fragment. 



FAMILY X.— BIDDULPHIEJS. 



Frustules cellulose, compressed ; lateral valves entering into the front view, 

 and usually more or less produced, at one or both angles, into processes. The 

 Biddulphieae are remarkable for the great development of the lateral valves of 

 the frustule, which are so convex or inflated as always to enter largely into 

 the front view, causing the central zone to appear like a* band between them. 

 The mode of growth in this family is very interesting. Instead of simple 

 elongation and subsequent division of the central zone by means of internal 

 septa, new central and inner lateral valves are formed within the elongated 

 original one, which, until ruptured, retains the frustules in pairs. The central 

 zone is at first very narrow and merely a broad line, but it increases greatly 

 in breadth until the new frustules are fully formed. 



Genus CERATAULUS (Ehr.). — Frustules with turgid lateral valves, each 

 valve with two tubular processes alternating with the same number of horn- 

 like spines ; lateral view orbicular or broadly oval. Cerataulus seems, in some 

 measure, to connect the Biddulphieae with the Eupodiscege, since, in a lateral 

 view, it approaches the latter in the cii'cular form of some of its species ; the 

 front view, however, is similar to the other genera of this family : the frus- 

 tules are binately conjoined by an external punctated sheath, and their pro- 

 cesses are definite in number. Ehrenberg describes the frustules as simple, 

 by complete fission ; but Professor Bailey finds them concatenate. Cerataulus 

 is characterized by having stout horn-like spines, which are not situated on 

 protuberances between the two processes, but alternate with them, and form 

 part of the same circle. 



Ceuataulus turgidus (E.). — Pro- 

 cesses short, broad, and truncate ; lateral 

 valves broadlv elliptic, with a submar- 

 ginal band of apiculi. EB. 1843, p. 270. 

 Biddnlphia turgida, SBD. ii. p. 50, pi. 62. 



f. 384; Ro TMS. vii. p. 17, pi. 2. f. 23. 



Europe, America. Professor Bailey thus 

 describes this species : — " Frustules glo- 

 bular or slightly compressed, with two 

 large prominences at each end, cohering 



