540 
SILURIA. 
A. Species with a single series of cells. 
a. Polyparies simple. 
1. Rastrites, Barrande. Cells free throughout their whole length. 
Containing 3 species. Example : R. maximus, Carruthers. 
Foss. 90. f. 6. 
2. Graptolithus, Linn. Cells in contact throughout more or less 
of their length. Containing 13 species. Ex. : G. priodon, 
Bronn. Foss. 12. f. 3. 
b. Polyparies compound. 
3. Cyrtograpsus, Carr. Polypary growing in one direction from 
the primary point. Containing 1 species: C. Murchisonii, 
Carr. Foss. 90. f. 1. 
4. Didymograpsus, M'Coy. Polypary growing bilaterally, and 
consisting of two simple or double branches. Containing 
10 species. Ex. : D. geminus, Hisinger. Foss. 9. f. 8. 
5. Dichograpsus, Salter. Polypary growing bilaterally and branch- 
ing regularly ; the non-celluliferous basis of the branches in- 
vested with a corneous disk. Containing 2 species. Ex. : 
D. Sedgwickii, Salter. Foss. 90. f. 3. 
6. Cladograpsus, Carr. (non Geinitz). Polypary growing bilate- 
rally, irregularly and repeatedly branching and rebranching, 
and without a central disk. Containing 2 species. Ex. : 
C. linearis, Carr. Foss. 90. f. 8. 
7. Dendrograptus, Hall. Polypary with a thick common stem, 
and branching irregularly. Containing 2 species. Ex. : D. 
lentus, Carr. Foss. 90. f. 5. 
B. Species with two series of cells. 
a. With a slender solid axis. 
8. Diplograpsus, M'Coy. Cells consisting of true hydrothecee. 
Containing 9 species. Ex. : D. pristis, His. Foss. 10. f. 15 j 
and Foss. 13. f. 14. 
9. Climacograptus, Hall. Cells hollowed out of the body of the 
polypary. Containing 3 species. Ex. : C. scalaris, Linn. 
Foss. 12. f. 4. 
b. "Without an axis. 
10. Retiolites, Barr. Containing 2 species. Ex. : R. Geinitzianus, 
Barr. Foss. 90. f. 2. 
C. Species with single and double series of cells on different parts of the same 
polypary. 
11. Dicranograptus, Hall. Containing 1 species : D. ramosus, Hall. 
Foss. 90. f. 4. 
13. Species with four series of cells. 
12. Phyllograptus, Hall. Containing 1 species : P. angustifolius, 
Hall. Foss. 90. f. 7. 
[In noticing the Silurian rocks of Sardinia (at page 422), I omitted to remark 
that General Albert de la Marmora's elaborate work, ' Voyage en Sardaigne ' 
&c. (1857), is enriched with a valuable appendix by Prof. J. Meneghini, descrip- 
tive of the fossils of that island, amongst which are many new species of Silurian 
Mollusks and of Graptolites, some of the latter being of very large size. — R. I. M.] 
