OF THE A:N-GULIFEE£JE. 



853 



stinction seems to be the marginal nodule of the former, — a character perhaps 

 overlooked by Professor Bailej. 



PLemidiscus cuneiformis (Wallich). — 

 Valves semilimate ; venter Tvdth a mar- 

 ginal row of puncta, and slightlv gibbous 

 at the middle. Wallich, TMS. viii. 



p. 45, pi. 2. f. 3, 4. Bay of Bengal and 

 Indian Ocean. Cellulation distinct, 

 largest at the centre. Connecting zone 

 broadest at the dorsum, (yr. 14.) 



Genus TEICERATIUM (Ehr.).— FrustulesceUulose, free, simple ; in lateral 

 view triangular (rarely with four or five angles). This genus has been well 

 illustrated by Mr. Brightwell in his excellent monographs published in the 

 ^ Journal of Microscopical Science ; ' so that the sj^ecies can be distinguished 

 without much difficulty. His discovery, in more than one species, of frustules 

 with four or even wdth five angles, shows that in this, as in several other cases, 

 the number of parts do not afford good generic distinctions. We were inclined 

 to place greater reliance upon their complete fission ; but Professor Bailey in- 

 formed us that he had met mth catenate specimens. Mr. Brightwell, indeed, 

 says that " the projection of a connecting membrane (central portion) beyond 

 the suture of the valve, which is one of the characters of the genus Amphi- 

 tetras, is not seen in the square forms of Triceratium ; " but we greatly doubt 

 the validity of this distinction. " One of the difficulties attending the study 

 of this genus, and the determination, especially in the fossil forms, of the 

 species, arises from the difficulty of obtaining perfect frustules, and examining 

 them in their front aspect. The imperfect frustules present only the end or 

 triangular wall, from which alone no j)erfectly satisfactory^ specific character 

 can be ol)tained " (Br.). 



The descriptions, unless otherwise specified, apply to the lateral \iew of 

 the frustules, and are drawn up, with few exceptions, from Mr. Brightwell's 

 monographs. 



* Lateral surfaces spinous. 



Triceratium spinosicm (B.). — Sides 

 nearly straight; angles prolonged into 

 horn-like processes ; granides mhiute ; 

 spines numerous ; front view constricted 

 beneath the processes. Silliman's Jour- 

 nal of Science, xlvi. pi. 3. £ 2. = T. seti- 

 gerwn, BC. 1854, pi. 1. f.24; T. armatum, 

 *Pvo MJ. ii. p. 283 ; T. tridacti/lum, Bri 

 MJ. i. p. 248, pi. 4. f 3. Fossil, Ame- 

 rica; recent, England, Florida, (vi. 

 19.) A variable species ; its numerous 

 spines and somewhat triradiate form best 

 distinguish it. Larger spines are often 

 interspersed among the smaller ones. 



T. cotnjKtctimi (Bri. MS.). — Spinous ; 

 fi'ont view constricted beneath the some- 

 what inflated processes ; central portion 

 bordered by a series of large cellules. = 

 T. armatum, /3, Bri MJ. iv. p. 274, pi. 17. 

 f 11. Recent. Australia. Smaller than 

 T. spinosum, but like it in form, having 

 a spine on the middle of each side. In 

 the front \'iew it is very different. 



T. comferum (Bri.). — " Sides uTegu- 

 larly concave ; angles drawn out into an 

 extended cone with a short, stout horn 

 near each : centre of frustule convex, 



with three setae." Bri MJ. iv. p. 274, 

 t. 17. f 6. Shell cleanings. The mani- 

 niillate angles, giving the sides a waved 

 appearance, mark the species. The gra- 

 nules are not radiant. 



T. contortum (Sh.). — Angles prolonged 

 into curved horn-like processes ; spines 

 in three radiate double rows, terminating 

 near each angle with a long bristle. Sh 

 TMS. ii. p. 15, pi. 1. f. 7. Recent. Natal. 

 (yi. 18.) Well distinguished by its con- 

 torted angles. Sides straight. 



T. orhiculatmn (Sh.). — Sides convex ; 

 angles obtuse, each with a circular 

 pseudo-nodule accompanied by a spine ; 

 gi-anules minute, radiating. Sh TMS. ii. 

 p. 15, pi. 1. f 6. Natal. The front view 

 shows the narrow central portion marked 

 like the lateral portions, which are large, 

 not constricted, and terminated by three 

 truncated cones. Mr. Brightwell enter- 

 tains no doubt as to the identity of his 

 specimens with Mr, Shadbolt's species ; 

 yet the latter's figure has no spines, and 

 he describes "the margin being so in- 

 flated as to cause the triangular outline 

 to approach that of the circle." 



T. Mari/landicum (Bri.). — Sides nearly 

 straight, with rounded angles, without 



