OF THE MELOSlREJi:. 



811 



the most part the Coscinodiscese are related to this family, with which they 

 have been hitherto united by Ehrenberg ; but I have separated them because 

 the shell of the Coscinodisceae often has divergently arranged bands and a 

 cellulose formation, which is wanting in the Melosirese. Moreover the forms 

 of the genus Melosira have in life so great similarity to the true simple Con- 

 fervae, that they may easily be confounded even by practical Algologists. 

 The heating of a specimen upon mica, however, distinguishes them so cer- 

 tainly that we can never be in doubt " (Kiitzing). The line of demarkation 

 between the Melosireae and Coscinodiscese is by no means well established ; 

 generally, discoid forms with cellulose structure belong to the latter, and fila- 

 mentous or smooth species to the former. This family, however, contains 

 some distinctly cellulose species ; but they are distingiushed by their inflated 

 or vaulted segments and the absence of a central portion. 



We have removed some genera Kiitzing had placed here, as we consider 

 Mr. Brightwell has proved that they are more akin to Chaetoceros. 



Genus CYCLOTELLA (Kiitz.). — Frustules discifoim, simple or binately 

 conjoined ; central portion ring-like ; valves plane or slightly convex. 

 Aquatic and marine. =Discoplea, Ehr. Cydotella differs from Melosira in 

 not forming a filament. The recent species, according to Kiitzing, are either 

 adnate or enclosed in a shapeless gelatinous substance. Some of the species 

 approach closely in character to Coscinodiscus. We retain Kiitzing's name 

 because it has the claim of priority. 



Cyclotella operculata (K.). — Valves j 

 depressed in the centre; strise obscure 



very short ; front view with rounded 

 angles. SBD. i. p. 28, pi. 5. f. 48. Fresh 

 water. Em-ope. This species is involved 

 in great confusion, and we confess our 

 inability to reduce it. We have adopted 

 Professor Smith's views, though with 

 much hesitation. Kiitzing describes the 

 margin as punctated; and his figm-es, 

 though varying much in size, of the 

 umbilical portion, show the margin 

 closely and irregularly pimctate, whilst 

 Smith describes them as striated. Kiit- 

 zing refers here the Discoplea Kiitzmgii 

 (E.) ; but that form, according to the 

 figures in the ^ Microgeologie,' is larger, 

 with radiating striae reaching to the 

 centre of the disc. (v. 53.) 



C. rectangula (Breb.). — Similar to C. 

 opei'culata ; but the frustules in the front 

 view have acute angles. Rah D. p. 11. 

 France. By Kiitzing made a variety of 

 C. operciilata, by Smith of C. Kiitzmgi- 

 ana. (v. 54.) 



C. Scotica (K.). — Frustules adnate; 

 disc plane, very smooth. KB. t. i. f. 2, 

 3. = C. Ligustica, K. /. c. t. 1. f 4. On 

 marine algae. Scotland, &c. We imite 

 C. Ligustica to this species, since Kiitzing 

 makes no distinction except size, which 

 in the Diatomacete is too variable to be 

 made the onlv specific difterence. D. 

 1-960" to 1-516". (xw. 17.) 



C. maxima (K.). — Frustules large, ad- 

 nate ; disc nearly plane, punctated. K. /. c. 



1. 1. f. 5. On Algae in the Pacific. Diam. 

 1-800" to 1-126". Puncta scattered. 



C. Coscmodiscus (E., K.). — Disc small, 

 irregidarly but densely and finely granu- 

 late, margin smooth. = Z)wcq/:>/m Cosci- 

 nodiscus, EM. pi. 33. 10. f. 1, 2. FossU. 

 United States. Habit of Coscinodiscus 

 ininor, rather turgid on the sides. D. 

 1-1728". 



C. Mammilla (E., K.). — Disc smooth, 

 umbonate in the centre ; sutm-e in front 

 view tiunid, produced at the margins. = 

 Discoplea Mammilla, EM. pi. 38. 22. 

 f. 1-3. Fossil. Patagonia. The suture 

 between the valves is ridge-like, and 

 consequently projects at the margins. 

 Rim of disc striate. Diam. 1-1728". 



C. umhilicata (E.). — Disc smooth, with 

 a central smooth xnmho. = Discoplea um- 

 hilicata, EM. pi. 35 B, B. £ 9, From 

 Atlantic deep soundings. Ehrenberg 

 describes this species as smooth, but 

 figures it with a punctated centre. 



C. Americana (E., K.). — Frustides in 

 front view turgid, vdth a transverse, tri- 

 carinated ring ; disc punctate in the 

 centre. KSA. p. 19. United States. 

 Diam. 1-660". 



C. physoplea (E., K.). — Disc smooth, 



except a circlet of large vesicular-looking 



granides round the centre. = Discoplea 



physoplea, EM. pi. 33. 17. t 8. Fossil. 



, Virginia. Diam. 1-1152". 



I 0. cojnta (E., K.), — Disc with a circlet 



I of small striae near the margin, and a 



crowded central mass of granules. = Z>?5- 



