constricted at centre; ends truncate, with a central rostrum;
striæ 24 in -001". Length of valve -0024" to -0027". Breadth of
valve -0012". v.s.
Bréb. in lit. May 1854.
Marine or brackish water. River Nene near Wisbeach, June 1854, Mr S
Smith. Near Saltcoats, July 1854, Hr. AÍraoíí.
This approaches N. granulata, Bréb. MSS., but has much finer and less
conspicuously mouiliform striæ.
49. Navicula Crabro, Ehr. Valve deeply constricted, panduri-
form ; extremities subacute ; striæ distinct, obscurely moniliform,
nitesceut, 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. Navícula
Pandura, Bréb. Diat. Cherb. fig. 4.
Marine. Stomach of Pecten, Coast of Sussex, and Kinsale Bay, Co. Cork
W. Sm. Fnth of Clyde ; Carrickfergus Bay, February 1855, Mr. Hennedy.
I do not know the characters upon which Ehrenberg has founded his
genus Biploneis, but see nothing iu this species to warrant its separation
from Navicula : its close alliance with N. didyma, and the moniliform character
of its striæ, 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; striæ obscure. Length of valve-0007" t o -0009". Breadth
of valve at constriction -OOOIS". Breadth of valve at lobes -0002".
v.s.
Fresh water. Bridge of Allan, August 1855, Dr. Arnott. Stirlingshire,
July 1855, Br. Greville. St. Abb’s Head, July 1855, Br. Balfour.
51. Pinnularia borealis, Ehr. Valve linear-elliptical, sometimes
with a slight central constriction; extremities rounded or sub-
truncate; costæ not reaching median line, 13 in -OOl". Length of
V . -0013" t o -0025". Breadth of V . -0003" t o -0004". v.v.
Ehr. iu 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. pl. iv. 13. P. Hebridensis, Greg. Mic. Journ
vol. ii. p. 28.
Freshwater. Grasmere, August 1853 ; Co. Cork, June 1855, &c., IF. Sm.
Mull Deposit ; River Spey ; Lough Leven, and Elchies, Bamffshire, Dr.
Gregory. Haverfordwest, April 1855, Mr. Okeden. Near Silverdale, Lancashire,
December 1855, Mr. Johnson. (Mont Dore, Auvergne, elev. 4000 feet,
June 1854, W. Sm.)
52. Pinnularia hemiptera, W. Sm. Valve linear-elliptical, with
rounded extremities ; costæ radiate, not reaching median line, 27
in -OOl". Length of valve -0026" to -0036". Breadth of valve
•0004" to -0005". v.v.
Navicula hemiptera, Kiitz. Bacill. xxx. II. ad specim. authen. quæ dedit cl.
De Brébisson.
Fresh water. Parham Park and Rackham Common, Sussex, August 1853 ;
Co. Cork, frequent, W. Sm. Falls of the Tummel, July 1854, Dr. Greville.
A very frequent form in subalpine districts ; often overlooked from its resemblance
to P. viridis, from which it is distinguished by its finer striæ and
narrower valve.
53. Pinnularia gracillima, Greg. Valve linear, constricted towards
the rounded extremities ; striæ submarginal, often abbreviated
towards the centre of valve, 27 in -OOl". Length of valve
•0016" to -0028". Breadth of valve -0002". v.v.
Var. ft. A larger form with attenuated extremities, v.s.
Greg. Mic. Journ. vol. 4. pl. i. 31. Grev. Ann. ser. 2. vol. xv. p. 5. Var. ft.
P. tenuis, Greg. Mic. Journ. vol. 2. pl. iv. 9.
Fresh water : often with the last species. Fell-end, Lancashire, Mr. Johnson.
Var. ft. Mull Deposit; Braemar, August 1854, Dr. Balfour.
The apparent absence of striæ from the centre of the valve, where they ofteii
become marginal dots, led me at first to name this species P. vaciva ; but I
am now disposed to regard this character as of little importance. The form
Navicula pisciculus, Ehr. Kiitz. Bacill. xxviii. 64, is perhaps identical with the
present.
I cannot specifically distinguish var. ft. from the ordinarj' form.
54. Pinnularia Polyonca, Bréh. Valve with a central and two
smaller intermediate inflations ; extremities capitate and rounded ;
striæ submargiual, 24 in -OOl". Length of valve -0016" to -0031".
Breadth at central Inflation -0003" to -0006". v.s.
Bréb. in Kiitz. Sp. Alg. p. 85. ad specimina authentica.
lata, Greg. Mic. Journ. vol. 2. pl. iv. 10.
Fresh water. Mull Deposit, Dr. Gregory.
Pinnularia undu