166 MB. W. WEST OK" THE FRESHWATER 



tt6. XaXTHIDIUM SIJBHASTIFERTTM, nov. sp. (PL XXII. fig. 4.) 



X. tarn longum quam latum, incisura mediana profunda 

 acutangula aperta ; semicelluhe oblongo-ellipticse, cum duo 

 spinis singulis divergentibus ad utrumque latus ; a vertice visse 

 ellipticae cum spina una exhibente ad apices ; a latere visa? rotun- 

 datse ; membrana lsevis in centro semicellularum incrassato. 



Long. 54 /x ; lat. sine spin. 50 /x; long. spin. 12*5-18 ju; lat. 

 istbm. 19 ju ; crass. 27 p. 



II. Lough G-uitane ; GJen Caragh. 



This is at once distinguished from all other species hitherto 

 described as British in bearing but two spines on each lateral 

 margin of each semicell, the central protuberance is also reduced 

 to a strong thickening of the membrane. From X. liastiferum^ 

 Turn. (Some New and Rare Desm., in Jo urn. Royal Micr. Soc, 

 Dec. 1885, p. 938, pi. 15. fig. 20), it differs in its non-angular 

 semicells, larger size, and in being destitute of the small apical 

 spines ; it differs from var. inevolutum, Nord. (Fr. Wat. Alg. of 

 New Zeal. & Austr. p. 43, pi. 4. fig. 24), in its want of angu- 

 larity, its larger size, and more elliptical end view. 



7. X. Smithii, Arch. (Pritch. Infi 

 I. Lakes, Clifden to Roundstone. 

 Castletown. 



Mt 



tfVar. collum, nov. var. (PI. XXII. fig. 5.) 

 Yar. spinis tribus ad angulos superiores ; marginibus laterab- 



bus et polis concavis, incisura lata et quadrata cum anguhs 



incisurae latae et quadratae rotundatis ; isthmo longo. 



Long, sine spin. 30 /z; lat. ad bas. semicell. sine spin. 25 \x\ 



lat. ad apic. sine spin. 20 fi ; long. spin. 5-7"5 \x ; lat. isthm. 9/x ; 



crass. 15 \x. 



II. Cromagloun. 



This is not a stage of division. 



fVar. variabile, Nord. (Fr. Wat. Alg. of New Zeal. Sf 

 Austr. p. 44, tab. 4. figs. 27-29.) 



Long, sine spin. 22*5-25 /x; long, cum spin. 23*5-27 /*; lat. 

 sine spin. 18-20 /z; lat. cum spin. 22-23'5/z; lat. isthm. 7'5- 

 8*5 fj. ; crass. 12-5-14 p. 



I. Near Oughterard; Clifden.— II. Cromagloun; Carrautuo- 



hill : Tore Mt. 



