Bacillariea^, PlagiogrammaceaD, Dimerograrama. 711 



ctse; pseudorhaphe siepe prteseiis; IVustula e zoiia couaectivali visa 

 rectangularia, sa^pe iu fascias conjuacta. 

 Ph::eophora grauuliformia, sparsa. 



Conspectus Generum 



Dimerogramma Ralfs. — Valvie nodulo centrali carentes, inilatu contractie- 



ve; frustula cohaerentia, e zona connectivali visa quadrangula. 

 Glyphodesmis Grev. — Valvie pseudorhaphe instructae, series transversales 



granulorum in areolis clathratis pr;vbentes ; pseudonoduli et centralis et 



terminales distincti. 

 Omphalopsis Grev. — Valvae cruciformes, striis transversis interruptis (non 



clathratis) ornatae; pseudonodulus centralis distinctissimus. 

 Plagiogramma Grev. [Heleromphala VAw. 1858?) — Valvaj spatio centrali 



hyalino (plerumque transversali) et pseudocello centrali saepius minutissi- 



mo donatas, costis paucis validis transversis instructte, rare ecostatse; pseu- 



donoduli terminales praesentes. 

 \? Diadesmis Kuetz. — Valvae saepe medio inflatae contractaeve; noduli cen- 



tralis et terminales (pseudonoduli) prominentes; pseudorliaplie subiude m- 



distincta (Frustula cohierentia). Cfr. inter Naviculaceas]. 



DIMEROGRAMMA Ralfs [1861] in Pritch. Inf. p. 790 (Etym. dis bis, me- 

 ros pars ei gram^na linea, littera), Rabenh. Fh Eur. Algar. I, p. 123, 

 V. H. Syn. p. 146, De-Toni Osserv. tasson. Bacill. p. 906, Deniiculce 

 sp. Greg., Denticellce sp. Jan. et Rabenh. — Frustula quadrangula, 

 in fascias arcte conjuncta, sub polis constricta; valvae undulatse, 

 transverse striatse, nodulo centrali destitutae, striis medio vitta vel 

 area longitudinali (pseudorhaphe) lata medio dilatata interruptis, 

 apicibus levibus. 



Sectio I. Frustula e facie connectivali visa medio plus minusve tumida sub 

 apicibus constricta (non pluries uadulata). 



1. Dimerogramma minor (Greg.) Ralfs in Pritch. Inf. pag. 790, Grun. 2876 

 in Wien. Verhaadl. 1862, p. 376, t. VII, f. 29, Rabenh. Fl. Eur. 

 Algar. 1, p. 123, V. H. Syn. t. 36, f. 10, 11 a, Denticula minor 

 Greg. Diat. of the Clyde p. 22, t. II, f. 35. — Parvum; frustulis 

 paucis in fascias conjunctis; valvis anguste rhombeo-lanceolatis, 

 11-13 ^. longis, costis 5V.j-7Vf> in 10 f- 



Hab. in aLaralash Bay et Loch Fine» Scoti^e (Gregory), in 

 fundo maris adriatici (Lorenz). 



2. Dimerogramma nanum (Greg.) Ralfs in Pritch. Inf. p. 790, t. IV, 2577 

 f. 33, Rabenh. Fl. Eur. Algar.. I, p. 123, V. H. Syn. t. 36, f. II, 

 Dimeregramma Gregorianum Grun. in Wien. Verhandl. 1862, 



p. 376, t. VII, f. 21-23, Deniicula nana Greg. Diat. of the Clyde 



