45 2 



TERPSINOE. 



Valve oval, elliptic, with coarse cells irregularly 

 hexagonal placed in rows radiating round a group 

 of central cells ; cells of process diminishing 

 gradually in size up to the end. Girdle face 

 elongated, trapezoidal, with conspicuous process, 

 valve portion having 1*5 rows of cells in 1 c.d.m. 

 Connecting membrane with cells in regular 

 longitudinal rows, smaller than those of the valve, 

 about 2*5 rows in 1 c.d.m. Length of valve, 5*5 

 to 2 1 c.d.m. 



Fig. 175^. Isthmia enervis. 

 Valve view. 



Marine, parasitic. Very rare in Belgium, and hitherto only found ill the washings of mussels. 

 England (W. Sin. ! Ralfs, Kitton, Mrs. Griffiths, Okeden) ; Ireland (W. Sm Dickie) ; 

 Channel Islands (Baxter Coll. No. 3825); France (Desmazieres) ; Finmark and Spitzbergen 

 (Cleve). 



I. nervosa Kutz. (Baa, p. 137, pi. 19, f. 5; W. Sm, S.B.D., ii., 



p. 52, pi. 47* ; H.V.H. Types, No. 485), plate 34, fig. 891. 



Differs from the preceding by interior costas, which consolidate the valve 

 and are very visible in the girdle face. 



Marine. Parasitic on other algae. Not yet found in Belgium, England (W. Sm. ! Kitton). 

 Ireland (O'Meara, Mrs. Lvon, Moore). Shetland Islands (Edmonstone), Denmark. Iceland 

 (C. Agardh). 



II. Hemiaulide^e. Valves sim- 

 ple or septate, often showing various 

 abnormal inflations or with apices 

 raised into a mucronate point. 



GENUS 117. TERPSINOE EHR., 



1843. 



Valves furnished with transverse costse, 

 without spines or any trace of pseudo- 

 raphe. Frustules showing in girdle view 

 transverse costae, capitate, resembling 

 musical notes. Frustules united in bands. 



a. 



Fig. 176. 

 Terpsitw'e music a. 



a. Valve view. 



b. Girdle view. 



