184 EQUISETACEAE, MARSILEOWEAE, 



consisting of many isodiametric cells lying one above another, and in S. 

 ornatum the cells which are near the surface are also prolonged into irre- 

 gular hairs. Closely allied to Sporocarpon is Traquairia, Carr. (Fig. 18, A), 

 which is distinguished from it by the structure of the outer layer of the 

 envelope, but agrees with it in all other points. Williamson's tenth 

 paper in the Philosophical Transactions gives a full account of this genus 

 and some beautiful figures. The inner or supporting leaf of the envelope 

 has on it long spines forming hollow cylinders with obtuse extremities. 

 These give rise at regular distances to lateral branches of like character to 

 themselves, and these may in certain circumstances branch very copiously 

 and anastomose, and thus present an extraordinarily complicated net-work 

 or sponge-like aggregate of hollow tubes, which is traversed in the direc- 

 tion of the radii by the much broader main canals formed by the spines. 

 These relations are shown with especial beauty in radial and tangential 

 sections of the case, such as are figured by Williamson l . Zygosporites, 

 Will., a genus which owes its name to its likeness in habit to the zygotes of 

 Cosmarium, may perhaps, judging from some figures of Williamson 2 , be 

 found to belong to our present group. But this form, like Oidospora 3 and 

 Calcisphaera, Sollas 4 found in the Carboniferous limestone in the neigh- 

 bourhood of Chester, distinctly requires further investigation. 



If now from this detailed statement of facts we turn to the different 

 explanations which these objects have received, we must observe first that 

 Carruthers' idea that they are Radiolariae, in support of which he appeals 

 to Traquairia, can scarcely be maintained. According to this view the 

 outer system of tubes must be homologous with the skeleton and the sup- 

 porting lamella with the rind of the central capsule ; the sarcode-body 

 perished of course before petrifaction, but some remains of it were pre- 

 served in the inner cells. Haeckel, to whom Williamson 5 had sent his most 

 important original preparations, assures us that there is no Radiolarian with 

 such structural conditions as we find in the remains in question. William- 

 son on the other hand sees in all these forms macrospores of Lepidodendreae, 

 and of allied forms which cannot be more precisely determined. He says 

 in the supplement to his paper 6 , that he has received through Mr. Binns 

 a series of sections of a ' crushed Lepidostrobus, in all of which Traquairiae 

 occur under such conditions as leave no doubt that they are the macrospores 

 of a Lycopodiaceous plant.' I have seen these preparations in his collection, 

 and I must acknowledge that small groups of Traquairiae or single Tra- 

 quairiae do lie inside many of the sporangia. But the whole specimen is 

 so macerated that these might well have found their way in from the out- 



1 Williamson (1), X, t. 18, ff. 86, 87. - Williamson (1), X, t. 19, f. 55. 3 Williamson (1), 

 IX, t. 25, f. 102. 4 Williamson (1), x, t. 20. * Williamson (1), x, p. 511. 6 Williamson (10), 

 t. 21, f. 82. 



