Philip : The Diatoms of the Sedbergh Distyict. 151 



a Gomphonema or Cocconeis swept by accident from its hold, 

 may, by the iise of its raphe, regain a position in which it may 

 •safely fix itself again, but such cases must be comparatively 

 rare. The majority live on in undisturbed security, and. as a 

 consequence, lose first the use of the raphe, and then the ra})he 

 itself. We find in many cases that it has disappeared from 

 that one of the valves by which the diatom has been anchored. 

 Eventually it will no doubt disappear from the other as it 

 has already done in many cases, and then we arrive at our 

 third sub-family, the Pseudo-Raphidieas.in which a blank space 

 interrupting the striation of the valve marks the line which was 

 formerly occupied by a raphe. Such forms as these are 

 specially adapted to inhabit the streams of Alpine districts, 

 and we find that they, along with the non-motile Raphidie?e, 

 constitute the bulk of the forms comprised in my Sedbergh 

 gatherings. Like the Raphidieae, the}^ have adopted various 

 methods of securing themselves. Some, as the Synedras, rely 

 on a long needle-like form, or, as Ceratoneis, on a hooked 

 shape, for entangling themselves in the meshes of algae ; 

 others, like Fragilaria and Meridion, attach themselves together 

 in ribbon-like bands, or, as Diatoma and Tabellaria, in chains 

 and rope-like filaments. The following list of species found 

 in the Sedbergh district, shows a predominance of this sub- 

 family when we bear in mind, not only that as compared with 

 the list of the Hull district in which the Pseudo-Raphidieae 

 constitute only about a fourth, but also that the mere number 

 •of species does not indicate the proportion of individuals. 

 Many of the motile Raphidieae are represented only by scarce 

 and casual forms, while the Pseudo-Raphidieae are the most 

 numerous part of each gathering. These gatherings were made 

 from Hebblethwaite Ghyll, Uldale Ghyh, Settlebeck Ghyll, 

 and also from some tanks on the slopes of the hill of Winder. 

 A single species [Fragilaria crotonensis) was found in the drink- 

 ing-fountain in the Market Place. 



LIST OF DL\TOMS OF SEDBERGH. 



Raphidieae (Motile). | ^Cymbella leptoceras Kutz. 



A HI phipleura pellucida Kutz. \ ,, microcephala Grun. 



Aniphova ovalis Kutz. I ,, obUisa Greg. 



Cynihella aequalis W. Sm. i *Encyonema caespitosum Kutz. 



,, affinis Kutz. I „ ventricosiwi Kutz. 



j ,, delicatiila Kutz. j Naviciila elliptica Kutz. 



,, /rtez7s Nacg. ,, xar.ovalis. 



* Abundant. + Rare. 



j.^10 Apl. I. 



