BRITISH DIATOMACE^E. 61 



nation given of it in page 7. I do not, however, put this forward as an 

 altogether satisfactory explanation of this curious process, nor do I feel able 

 to account for the frequency of its appearance in genera and species so widely 

 different as Himantidium Soleirolii and Orthosira Dickieii ; I only desire to 

 record my impression that the process is not connected with the formation of 

 sporangia, and to commend it to the study of future observers. 



Plate LII. 335. 



4. Orthosira orichalcea, W. Sm. Filaments direct ; valves punc- 

 tate ; line of junction with more or less distinct subdistant denti- 

 culations; junction-surfaces smooth. Breadth of filament "00025" 

 to -0012". v.v. 



Melosira orichalcea, Melosira Italica, et Melosira Italica var. /3. crenulata, 

 Kiitz. Bacill. ii. 14, ii. 6, et ii. 8, ad specim. quae dedit am. De Brebisson. 

 M. orichalcea, Ralfs, Ann. vol. 12. pi. ix. 6. Hass. Alg. xciii. 6, 7. ad 

 specimina authen. in Herb. Jenn. Aulacosira crenulata, Thw. Ann. 

 2nd ser. vol. 1. pi. xi. B. ad specim. authen. quse dedit cl. Auctor Mar. 

 1847. Prit. Anim. xxiv. 33. Gallionella orichalcea, Ehr. Inf. x. 6. 



Fresh water. Cheshunt, Mr. Hassall. Aberdeenshire, June 1 848, Dr. Dickie. 

 Saltcoats, June 1854, Dr. Arnott. Well at Seven Churches, Clonmacnoise, 

 July 1855. Moanarone, Co. Cork, October 1855, W. Sm. Premnay and 

 Cantyre Peat ; Lough Mourne Deposit and Dolgelly Earth. (Falaise, M. De 

 Brebisson. Mont Dore, elev. 4500 feet, June 1854, W. Sm.) 



In different stages of growth this species presents much diversity in the 

 length and breadth of its frustules, and the greater or less distinctness of its 

 denticulations ; hence has arisen much confusion in the synonymy ; but a 

 careful comparison of specimens leads me to place together all the above 

 forms. To the same species might probably be referred a large number of the 

 forms given in the ' Microgeologie ;' the absence of descriptions in the latter 

 work, however, precludes me from attempting to give synonyms from it except 

 in those cases when the figures are sufficiently characteristic as to preclude 

 mistake. Sporangia are not frequent in this species ; but I have found a few 

 in the gathering from the Co. Cork. 



Mr. Thwaites, whose figures I have copied in Supp. Plate E. 327, has 

 described the sporangia as being formed at a distance from the parent valves, 

 and " with their axes of elongation (longest diameter) at right angles to the 

 frustule from which they originate." The peculiarity thus noticed would, if 

 established by observation in other species, constitute a good generic distinc- 

 tion : I regret to say that my experience does not enable me fully to confirm 

 the facts mentioned by Mr. Thwaites, and that I am therefore precluded from 

 adopting them as indications of generic differences. 



Plate LIII. 337. 

 5. Orthosira spinosa, n. sp. Filaments curved, often zigzag, from 



