188 THE POTOMAC OK YOUNGER MESOZOIG FLOKA. 



These stems liave a number of features in common witli Bennettites, but 

 do not fully agree with that genus. Compared with Mantellia Brongn., 

 Cycadcoideu, Ijuckland, they show some points of resemblance. Carruthers 

 says of ManteUiu trunks that they are cylindrical, covered with the long 

 permanent bases of the petioles, and have the fruits borne on secondary 

 axes which generally protrude beyond the bases of the petioles. In this 

 feature these secondary axes resemble Tysonia, and not, according to 

 Carruthers, Bennettites. The axillary branches in Mantellia, like those of 

 Tysonia, are broken off at the point where they leave the bases of the 

 petioles. Carruthers says that some of the branches in Mantellia are 

 undeveloped and still exist as unexpanded leaf-buds ; and this seems to be 

 the case with some of those of Tysonia, those that have little or no woody 

 axis. Some of the stems of Mantellia have no lateral buds, and they may, 

 as Carruthers says, be male stems, their staminal flowers being on cones 

 borne on the termination'of the main axis. The Potomac stem No. 2 has 

 no axillary buds, and shows indications of having borne a terminal ap- 

 pendage (bud?) by the side of the terminal growing leaf-bud. Carruthers 

 says that the Mantellia trunks were cylindrical, their flattened condition 

 being due to pressure. 



From this it will be seen that the stems of Tysonia have a number 

 of points in connnon with Munfelliu. They stand nearer to this than to 

 Bennettites. The shape of the trunk is more that of Bennettites, but in the 

 shape of the bases of the petioles and in other features Tysonia more 

 closely resembles 3Iantellia. 



In describing the new species Tysonia Marylandica, it is best to notice 

 the two nearly complete stems separately, as they are typical and show- 

 some important points of difference. I will describe them as trunk No. 1 

 and trunk No. 2. One of these was found, as stated before, near Contee's 

 station, in an iron-ore pit near the base of the Variegated Clay formation, 

 and one was found on a farm near Beltsville, a locality a few miles south 

 of Contee's. A fragment like trunk No. 1 was found with this trunk, and 

 another fragment like trunk No. 2 was found on the surface of the Varie- 

 gated Clay group at a locality (Spring Garden) in the outskirts of Balti- 

 more. It is impossible now to tell which of the trunks was found near 



