Geology and Natural History. 437 



with these fossils. The author's convictions are however often 

 apparent, even when not enforced. For example, he adopts the 

 term Triniwleus, though expressing the opinion that Dr. Green's 

 Cryptolithus is entitled to acceptance ; again the genus Acidaspis 

 is retained in its broad and current usage, though Captain 

 Vogdes himself has at an earlier date warmly and justly espoused 

 the precedence of Warder's term, Ceratocephala / in these and 

 other instances evincing his consideration for the convenience of 

 those who will make the most use of the work. But two new 

 generic names are proposed, Lloydia (in honor of Edward Llhwyd 

 " the first author on Trilobites ") for the species Bathyurus 

 bituberculatus Billings, and Strigocaris, in place of Solenocaris 

 Meek, a preoccupied term. The catalogue of non-trilobitic genera 

 is preceded by a scheme of classification which is open to objec- 

 tion in some respects. The author does not choose to recognize 

 Packard's order Phyllocarida, but divides the Phyllopoda into 

 the Ceratiocaridce, Discinocaridw and Rhinocaridw and in the 

 last family are placed PJstheria, Leaia and Schizodiscus (perhaps 

 the only genuine phyllopods in the list) as well as the genus 

 Mesothyra, which belongs to the distinct family, Pinacaridm. 



The entire work is unfortunately abundant in typographical 

 errors, few, however that need cause serious annoyance. Some of 

 these have already been corrected in a supplement issued by the 

 author privately, and it may be expected that others will be 

 eliminated in the future editions which, it is hoped, so valuable a 

 catalogue will attain. j. m. c. 



10. On the Organization of the Fossil Plants of the Coal-Meas- 

 ures ; by W. C. Williamson. Pt. XVII. Phil. Trans. Roy, 

 Soc. London, vol. 181. 1890, B, pp. 89-106, pi. XII-XV.— Part 

 XVII of this series of valuable memoirs is important for the evi- 

 dence which it contains of the discovery of an exogenous devel- 

 opment among the Carboniferous ferns. The anticipation ex- 

 pressed by the author in Part IV that Dictyoxylon (Lyginoden- 

 dron) Oldhamium, there described as belonging to Paleozoic 

 Proto-gymnosperms might be identical with the petioles described, 

 at the same time, as Edraxylon, and later (Pt. VI) as Rachiop- 

 teris aspera, is now confirmed, and the two are conclusively 

 proved to be trunk and petiole of the same plant. The origin of 

 the trachseal bundles of the petiole in the middle cortex of the 

 trunk and the formation of the medulla in the center are described 

 with the author's customary accuracy and minuteness of detail. 

 As the medulla expands during the growth of the petiole, there is 

 a corresponding increase in the number of vascular laminae, the 

 inner extremities of which, though commencing their growth at 

 different periods of life, all start from the medullary border of the 

 vascular zone and extend to the periphery. The number of these 

 laminaB were observed to vary from 44 in a small specimen, in 

 which the medulla was present, to 1120, similarly arranged, in a 

 large one. Not only has Prof. Williamson examined many speci- 

 mens showing the transition stages between the two types, but 



