BRITISH DESMIDIEJ5. 101 



Piltdown Common ; Midhurst ; Ashdown Forest, near Tmibridge Wells, 

 &c. ; Hampshire ; Sussex ; Reigate, Surrey, Mr. Jennei'. Dolgelley, J. R. 



Falaise, Brebisson. 



Frond compressed, larger than that of Cosmarium margaritiferum, deeply 

 constricted at the middle, the constriction producing a linear notch on each 

 side. Segments rather broader than long, semiorbicular, rough with pearly 

 granules or spines, which are longer than broad. The transverse view is 

 elliptic. 



I am not sure that this form is sufficiently distinct from Cosmarium mar- 

 garitiferum, as the specific difference chiefly depends on the elongated pearly 

 granules, a character which I fear is inconstant. 



Our specimens do not agree exactly with a drawing sent me by M. De Bre- 

 bisson ; but in specimens received from him the spines are less crowded than 

 in his figure. He informs me that " Le Cos. Brehissonii est plus globuleux 

 que le C. margaritiferum, et herisse de papilles inegales plutot que de tu- 

 bercules*." 



Length of frond y^-g- of an mch ; breadth of segment j^ ; length of mar- 

 ginal spine yaVs- 



Tab. XVI. fig. 3. a. empty frond ; b. side view. 



16. C.conspersum ; frond rough with depressed granules ; seg- 

 ments quadrilateral; end view elliptic. 



Dolgelley, J. R. Henfield, Mr. Jenner. 



Frond compressed, larger than that of Cosmai'inm margaritiferum and 

 having at the middle a deep constriction, which makes a linear notch on each 

 side ; segments rather broader than long, quadrilateral, rough with pearly 

 granules, which give a dentate appearance to the outUne. The transverse 

 ^iew is elliptic. 



Cosma7-ium conspersum diifers from C. margaritiferum and C. Brebissonii 

 in its quadrilateral figure and in ha^-ing its granules (which are more depressed 

 than those of C. Brebissonii) arranged in lines. In the front view its form 

 is not unlike some states of C. biretum ; but in that species the granules are 

 smaller, and the end margin is more prominent and generally flattened at the 

 centre. 



I formerly considered this plant to be the C. Brebissonii, vpith Meneghini's 

 description of which it certainly agrees better than a specimen so named which 

 has been sent me by M. De Brebisson. 



Length of frond -g-g-j- of an inch ; breadth at constriction -^^ ; breadth of 

 segment ■^. 



Tab. XVI. fig. 4. a. empty frond; b. transverse view. 



* I add Meneghini's characters of the two species : — 

 " C, margaritiferum, cellulis e dorso elhpticis, e latere semiorbicularibus, su- 



perficie granulatb-margaritifera." 

 " C. Brebissonii, cellulis e dorso elongato-ellipticis, e latere introrsum curvatis, 

 formam trapezii prse se ferentibus, superficie granulato-margaritacea." 



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