SPECIES OF riSIDIUM. ^i 



moderately swollen (PI. XXII, f. 16) but frequently tends to become 

 considerably so (PI. XXII, f. 17). This latter feature is frequent 

 in Irish specimens, which often attain a large si/.e in localities 

 Avhere the associated species of the genus are undersized. One of 

 the most elongate examples seen came from Salisbury (PI. XXII, f. 2) 

 and coming from running waters has the hinge strongly developed 

 in contrast to those from quieter waters as Lochmaben (PI. XXII, 

 f. 8) and Bracebridge (PI. XXII, f. 7), which are both less elon- 

 gate and weak in the hinge, whilst examples from llhosneigr 

 (Anglesey) (PI. XXII, f. 6) are comparatively round. Fossil 

 examples from the Strand, Xewbnry, and from (iayfield, Edinburgh, 

 have the umbones greatly developed, and so to a less extent has the 

 figured recent specimen from Gloucester (PI. XXII, f. 26). 



DISTRIBUTION. 



31 

 01 



NS CA 

 HB S3 



RW RE EL BF AN 

 Wl El PN AS 

 AW PM FF Kl 

 M DN 86 PC KF 



1 CT RF LL E_D HO 



AY LA PE BW NN 



WO EO 10 AH WT KB DF SK RX SN 



FE TY AR CU WL NY DM 



WM SL IE" MO ' M ML MY EY 



EM RO CV LH A SL WY SY L 



*6 N6 LF WH ME CR DB FT DY NM LS 



SG KC KO DU MN Mli SP ST LR B WN |N 



CL NT QC CW wi CD RA HF *<> NO Hy WS ES 



NK LK ST KK * x PBCMBR 6E 15fBDHTN| 



SK MC EC WA 6M MM GW NW * ^X^S_E 



wc MS SW Ntf SR~WK EK 



ND 88 DT SH w_X EX 

 EC 3D '* 



8C WC 



Cl 



Piridium subtrvncatum . 



(Recent occurrences are shown in red : fossil occurrences by a line 

 below the symbols. For the explanation of the symbols see p. -JO.) 



