Article: The ventral anatomy of the Upper Carboniferous eurypterid Anthraconectes Meek and Worthen

All the known species of Upper Carboniferous eurypterids appear to have had so similar a dorsal anatomy that they have been thought to belong to one genus which has gone under three names. Of Adelophthalmus Jordan and von Meyer 1854, Lepidoderma Reuss 1855 and Anthraconectes Meek and Worthen 1868, only the last is founded on a specimen showing both the ventral organs (in the holotype) and the dorsal (in the counterpart). Anthraconectes is therefore preferred (though the other names have priority) until it is known whether the ventral anatomy of either of the others is the same as that of Anthraconectes.The ventral anatomy of the genus is described from the holotype and topotypes of A. mazonensis Meek an Worthen and A. moyseyi H. Woodward. Particular attention is paid to the 1st or genital operculum as revealed in the natural casts and in etched specimens. Sexual dimorphism is described and deductions made fror several examples displaying Stormer's Type A median genital organ and two showing his Type B. In Type A the 1st and 2nd opercula resemble Type A of Eurypterus fischeri Eichwald, as described by Holm 1898 and by Wills 1964. Type B is less well documented, but one specimen of this type is shown to resemble Type B of E.fischeri in having clasping organs. Internal evidence indicates that Type A was the female and Type B the male as was claimed by Holm to be the case in E. fischeri.Nothing was discovered about the structure of the gills or their position on the body, except that there are small spots devoid of scale-ornament on the opercula, which may provide an indication of the positions on the roofs of the overlying gill-pouches where, by analogy with Eurypterus, the gills themselves were sited.