NATURAL SCIENCES OF PHILADELPHIA. 63 



■Report Regents on State Cab., N. H., pi. ii, fig. 12); but its pecu- 

 liar posterior dorsal sulcus, which gives it so much the appearance 

 of the recent L. Jamaicensis^ is neither represented in Mr. Conrad's 

 figure, nor mentioned in his description of L. lirata. 



The identity of these Devonian shells with the existins: aenus 

 Lucina may admit of some doubt, as their hinges and internal 

 characters are not yet well known. The species under considera- 

 tion, however, has even more exactly the external appearance of 

 that genus than several foreign Devonian forms that are generally 

 referred to it. Perhaps they may all be included under one dis- 

 tinct genus, for which the name Paracyclas, Hall, may have to 

 be retained. 



Locality and position. Dublin, Franklin Co., Ohio. Coraiferous 

 division of the Devonian. 



■PTILODICTYA (STICTOPORA) GILBERTI, Meek. 



Corallum growing in thin, or much compressed, branching (or 

 perhaps sometimes foliaceous) expansions ; branches var3-ing 

 from about half a line to three lines in breadth, with a thickness 

 of near half a line; nonporiferous margins sharp, with strios well 

 defined, and curving laterally and forward. Pores nearly circular, 

 or slightly oval, and provided, in well-preserved specimens, with 

 raised margins ; ranged in about eight to ten longitudinal rows 

 in a branch two and a half lines in breadth, those in adjacent rows 

 regularly alternating so as to produce a quincuncial arrangement; 

 five of them occupy a space of one line, measuring longitudinally, 

 and about six measuring obliquely, the spaces between the pores 

 in the longitudinal direction being usually a little greater than 

 the diameter of the pores themselves ; rows of pores separated by 

 a slender, sharply raised longitudinal line. Axis forming about 

 one-third of the thickness of the branches, and having the trans- 

 verse strife sometimes very regular, well defined, and regularly 

 arched. 



I have not seen enough of any one specimen of this species to 

 show whether or not its branches anastomose, but as they evi- 

 dently frequently bifurcate, and send oflf lateral branchlets, it is 

 probable that they do. It seems to be more nearly allied to 

 Stictopora fenestrata, of Hall, from tht Chazy limestone, in the 



' This description was accidentally inserted iu this place. 

 1871.] 



