OF THE MERIDIEM. 767 



with the latter, for he '' does not consider the cuneate form of the frustnles 

 of any valne in an organological point of view," because of the occasional 

 occiuTences of such fmstnles in Diatoma and other genera of the Fragilarieae. 

 In the latter family, however, the cuneate frustulcs, when present, are in 

 general interposed between those of the normal shape, and the lateral surfaces 

 have not dissimilar extremities. Kiitzing observes that " the forms of this 

 family have very great similarity to those of Gomphonema, with which they 

 may be the more easily confounded when the indi\iduals occur singly ; but 

 they are essentially distinguished from that genus by not having a central 

 nodule in the secondary sides, and by their uninterrupted transverse striae. 

 Moreover, this family is much more closely united to the genus Odontidium, 

 from which it is distinguished solely by the form of the secondary sides, 

 which are not symmetrical at both ends." AVe, however, consider its affinity 

 with the Licmophoreae still more evident. The Meridiea?, Licmophoreae, and 

 Gomphonemese " form a group [the Styllarieae of Agardh] distinguished by 

 the triangular form of the frustules, which have their smaller ends directed 

 towards a common centre. The frustules in this group have a central and 

 two lateral portions, as in Diatoma and Fragilaria, in which genera cuneate 

 frustules are also occasionally met with. But in the Fragilarieae, when two 

 or more cuneate frustules are united, the alternate frustules have their 

 smaller ends in opposite directions, and hence their filaments are linear; 

 whilst they are attached, if at all, only by the basal frustule. In this group, 

 on the contrary, as the smaller ends are in the same direction, they point to 

 a common centre, and when stipitate, each frustule is attached to the stipes " 

 (Ealfs). The frustules in the Meridieae have two pun eta at the broader end, 

 and sometimes other two, but more obscui'e, at the smaller end ; they want, 

 however, the sutural or fracture -like longitudinal lines which are present in 

 the Licmophoreae. 



Genus MERIDION (Leibl., Ag.). — Frustules cuneate, imited in a spiral 

 filament ; transverse costae of lateral siu"faces pervious. " The species vary 

 according to the circumstances of development, as well with respect to size 

 as to other relations. The individuals are met with both singly among other 

 Algae and also in masses. At times examples are found which are always 

 composed of only few individuals ; others again consist of individuals united 

 in greater number ; but generally the longer spiral ribands are rare." (Kiitz.) 

 Professor Kiitzing formed a new genus (Eumeridion) for the reception of 

 M. constrictum ; but his reasons have been considered inadmissible by De 

 Brebisson, Meneghini, and Smith. Meridion is remarkable for the frequent 

 occurrence within its frustules of an obovate silicious ceU, which is usually, 

 but not invariably, divided into two symmetrical portions by a longitudinal 

 suture ; the lateral margins of the inner cell, as well as the sutiu'al line, are 

 crenulate like those of the original frustule. The different aspect presented 

 by specimens in this condition has induced some observers to describe them 

 as a distinct species. A\TiLlst we agree with Professor Smith that the modi- 

 fication is insufficient to warrant such a separation, we cannot coincide with 

 him in regarding it even as a variety, since frustules with these internal ceUs 

 are indiscriminately mixed mth ordinaiy frustules in the same filament. So 

 common, indeed, is this occuiTence, prior to the termination of individual hfe, 

 that we have long been convinced that it is the normal mode of termination 

 in this genus. 



= 31. vernale, E. ; M. Zinckeiii {vnth. in- 



Meridion circulare (Grev., Ag.). — 

 Frustules iu lateral view clavate or 

 obovate. SBD. vol. ii. p. 6, pi. 33. f. 277. 



temal cells), KB. ; B. curvatum, K. 

 Frustides slightly arcuate. Common, 



