94 BRITISH DIATOMACEjE. 



constricted at centre ; ends truncate, with a central rostrum ; 

 striae 24 in -001". Length of valve -0024" to -0027". Breadth of 

 valve -0012". v.s. 



Breb. in lit. May 1854. 



Marine or brackish water. River Nene near Wisbeach, June 1854, Mr. S. 

 Smith. Near Saltcoats, July 1854, Dr. Arnott. 



This approaches N. granulata, Breb. MSS., but has much finer and less 

 conspicuously moniliform striae. 



49. Navicula Crabro, Ehr. Valve deeply constricted, panduri- 

 form ; extremities subacute ; striae distinct, obscurely moniliform, 

 nitescent, 10 in -.001". Length of valve -0027" to -0040". Breadth 

 of lobes -0013"; ditto at constriction -0008". v.s. 



Ehr. in Kiitz. Sp. Alg. p. 83. Diploneis Crabro, Ehr. Microg. xix. 29. Navi- 

 cula Pandura, Breb. Diat. Cherb. fig. 4. 



Marine. Stomach of Pecten, Coast of Sussex, and Kinsale Bay, Co. Cork, 

 W. Sm. Frith of Clyde ; Carrickfergus Bay, February 1855, Mr. Hennedy. 



I do not know the characters upon which Ehrenberg has founded his 

 genus Diploneis, but see nothing in this species to warrant its separation 

 from Navicula : its close alliance with N. didyma, and the moniliform cha- 

 racter of its striae, which, though obscure, is to be detected with careful 

 manipulation, leave no doubt of its position. 



50. Navicula trinodis, n. sp. Valve with a double constriction, 

 dividing its surface into three nearly equal lobes ; extremities 

 rounded ; striae obscure. Length of valve 'OOO/" to *0009". Breadth 

 of valve at constriction *00013". Breadth of valve at lobes -0002". 



v.s. 



Freshwater. Bridge of Allan, August 1855, Dr. Arnott. Stirlingshire, 

 July 1855, Dr. Greville. St. Abb s Head, July 1855, Dr. Balfour. 



51." Pinnularia borealis, Ehr. Valve linear-elliptical, sometimes 

 with a slight central constriction; extremities rounded or sub- 

 truncate; costae not reaching median line, 13 in -001". Length of 

 V. -0013" to -0025". Breadth of V. -0003" to -0004". v. v. 



Ehr. in Kiitz. Bacill. xxviii. 68 & 72. Raben. Siissw. Diat. vi. 19. Ehr. 

 Microg. passim. Greg. Mic. Journ. vol. iv. p. 2. Pinnularia late-striata, 

 Greg. Mic. Journ. vol. 2. pi. iv. 13. P. Hebridensis, Greg. Mic. Journ. 

 vol. ii. p. 28. 



