56 Prof. T. R. Jones and Mr. J. W. Kirkby on 



and a slight rim bouiuliiig the tree iiiari;ui : the surfaee, In 

 lunvorn exani[)les, i.s retieuhitely omanieuted, and is u.sually 

 marked witli minierous rather line lonuitudinal Avriukles, 

 due to the thiekening of the longitudinal walls of the net- 

 work. 



The Ui)per-Silurian P. rnn'olata, J. ct II. op. cit. \k 418, 

 j)l. 13. f. (3, i.s a near ally ; but is shorter, has its suleus more 

 central, and shows only a pitted ornament. 



Some small bivalve carapaees from the Carboniferous strata 

 of West Scotland t, and others from Shropshire, are allied to 

 the form under notice, having suboblong outline, longitudinal 

 wrinkles (stronger), and some fine reticulation ; but the sulcus 

 is contracted to a central jn't, such as is found in some Primitife. 

 We have also a small smooth form from Lanarkshire. 



4. Bairdia cequalis, D'Eichwald. PI. VI. fig. 4. 



We identify a specimen from the yellow limestone of Likh- 

 wine with this species. It is ^^^ inch long, ^^ inch high, 

 smooth, swollen, of a subtrapezoidal outline, with the pos- 

 terior extremity blunt, and with a strong dorsal and ventral 

 overlap. 



5. Bairdia ampla^ Reuss. PI. VI. tig. 5. 



Two very fine examples of a Bairdia sent us by M. d'Eich- 

 wald as B. carta, from Sloboda, in the Government of Toula, 

 appear to us to belong to B. ampla, Reuss, known in both the 

 Carboniferous and Permian formations. 



The perfect shape of B. carta, M'Coy, has been given by 

 one of us in plate 61. fig. 1, ' Monthly Microsc. Journ.' vol. iv. 

 1870. 



6*. Bairdia plebeia, Reuss, var. rhombica, Jones. 

 PL VI. fig. 6. 



Included with the specimens of the last species is a single 

 example of what seems to be, if not a distinct species, a 

 rhombic variety of B. pleheia, described and figured in the 

 ' Trans. Tyneside Nat. Field-Club,' vol. iv. 1859, p. 42, pi. 11. 

 figs. 10, 11, 12. B. pleheia is common in both the Carboni- 

 ferous and Permian formations ; var. rhombica is Permian also. 



+ '^Kirkbi/a scotica," J. & K. MS., ' Trans. Geol. Soc. Glasgow,' vol. iii. 

 Siippleni. (.'arb. Foss. p. 28. Unless specinien.s with concentric longitu- 

 dinHl rib^ occur, this species will have to be allocated to Pn'/ntlia. 



