THE FBESHWATEE ALG^ OF MADAGASCAR. 53 



Long. 36-39 ^ ; lat. 26-5-28 ^ ; lat. lob. pol. 10 5-17-5 ^ ; lat. isthm. 6 ^; crass. 16 ^. 



IN O. o. 



51. Etjastrum pyhamidatum, West, Preshw. Alg. of W, Ireland, p. 139, pi. xv. fig 13. 



Var. INCRASSATUM, nov. var. (PL VI. fig. 20.) Var. paullo major, semicellulis in medio 

 incrassatis. 

 Long. 32 ^ ; lat. 20 ^ ; lat. isthm. 6 ^ ; crass. ISo /i. 

 No. 0. 



Compare with Cosmarium mhlohatum. Arch., var. crispulum, Nordst. (Bidrag till 

 kannedom sydlig. Norges Desmid. p. 10, fig. 9). 



52. EuASTRUM BiNALE, Ealfs, Brit. Desmid. p. 90, tab. 14. fig. 8. 



Long. 17 A*; lat. 15 ^u; lat. isthm. 4-5 ^ ; crass. 8-5 ^. (PI. IX. fig. M.) 

 No. 0. 



53. Efastrum denticulatum, F. Gay, Sur les Conj. du Midi de la France, 1884, p. 335. 

 Long. 16-28 n ; lat. 12-20 ^ ; lat. isthm. 3-55 ,u ; crass. 13 ^. (PL IX. figs. 15, IG.) 

 Nos. and 1. 



Var. RECTANGULARE, noY. var. (PL VI. fig. 21.) Var. apicibus et basibus semicellularum 

 sequilatis, granulis paucioribus, tumore central! sine granulis. 



Long. 22^; lat. ad bas. semicell. IT'S/*; lat ad apic. 17^; lat. isthm. 5 5 ^\ 

 crass. 10 ^u. 



No. 3. 



54. EuASTRrM TRIGIBBERUM, nov. sp. (PL VI. fig. 22.) E. parvum, paullo longius 



quam latum, in medio profunde constrictum, sinu lineari ; semicellulae truncato- 

 pyramidatoe, triloba^, incisuris lateralibus apertis et subprofundis ; lobis lateralibus 

 subquadratis in margine 4-granulatis ; lobo polari latissime subrectangulari, lateribus 

 bigranulatis, angulis superioribus in spinam productis, apice 4-granulatis incisura 

 mediana alta ; semicellulse tumore mediano granulis quinque ornato, tumore 

 utrobique granulis qnatuor ornato, seriebus duabus horizontalibus granulorum 

 quatuor intra lobum polarem; a vertice visse elliptica?, tumore magno utrobique 

 medio trigranulato ad apicem truncatum, prope polos utrobique tumore emarginato, 

 polis trigranulatis ; a latere visae trilobae, lobis lateralibus apice truncato tri- 

 granulato, lobo polari lateribus bigranulatis apice spinjk ornato. 



Long. 23 iu; lat. lO'S /i ; lat. lob. poL 14 ^; lat. isthm. 65^; crass. 135 /i. 



No. 18. 



The nearest species to this is E. denticulatum, F. Gay, from which it differs in the 

 deep lateral incisions of the front view, in the three basal tumours well seen in the 

 vertical view, as well as in other characters. 



