326 Prof. Bailey on Fossil and Recent Infusoria. 



spinularum aut membranacea erecta externa in ipso cujusvis valvulse 

 disco, (nee in ipso margine.)" 



This genus has the habit of Cosdnodisciis lineains, but with 

 lateral crowns, which in the young state connect two individuals. 



5. " ScEPTRONEis, nov. gen. — Animal e Bacillariis Echinelleis ? affix- 

 um ? Lorica simplex sequaliter bivalvis silicea stiliformis compressa, 

 non concatenata, cuneata, (viva facile pedicellata.) Sutura laterum 

 utriusque valvre longitudinalis media, umbilicus nuUus," 



The only species, Sceptroneis Caduceus, is represented in fig. 

 11. It resembles a Gomphonema, but wants the lateral umbili- 

 cus. In the fossil state it is impossible to decide whether it was 

 fixed to a pedicel when living. It occurs in myriads in the Ber- 

 muda Tripoli. 



6. DicTYOPYXis, nov. suhgen. — This subgenus is formed to in- 

 clude those species of the old genus Pyxidicula which have a 

 cellular surface. PI. II, fig. 2, in Vol. xlii, of this Journal, repre- 

 sents a species from Richmond, Ya. now called Dictyopyxis cru- 

 ciata. 



7. " Mastogonia, nov. gen. — Animal e Bacillariis Naviculaceis libe- 

 rum. Lorica simplex (in^qualiter) bivalvis, non concatenata, valvis 

 siliceis angulosis mammiformibus, basi orbiculari, umbilico inermi. 

 Valvularum membrana continua integerrima nee cellulosa, angulis ra- 

 diantibus." 



These forms, which were formerly placed in the genus Pyxi- 

 dicula, may be recognized by having an orbicular base, connect- 

 ed on each side by radiant lines, with an unarmed central and 

 elevated umbilicus, and by having a smooth surface. To this 

 genus is now referred (without change of specific names) the 

 two species Pyxidicula O cuius- Chamceleontis and P. Actinop- 

 tychus, Ehr. from Virginia. A species, Mastogonia heptagonce, 

 Ehr. is represented in fig. 12. The number of radiant lines in 

 this genus varies very much, and Ehrenberg states that it is 

 sometimes different on the two sides of the same individual. 



8. Stephanogonia, nov. gen. — This genus has the characters 

 of Mastogonia, but in addition has also a row of projecting spines 

 around the umbilicus. Ehrenberg describes two species, the 

 first, iS. quadrangula, discovered by himself, and the second, S. 

 polygona, founded on an outline sketch which I sent him of a 

 form noticed by myself in the Bermuda Tripoli. This is repre- 

 sented in fig. 13. 



