WAVERLY GROUP SRECIES. 



MOLLIJSCA. 



POLYZOA. 



Genus FENESTELLA, Loupdale, 1837. 



(Murchison's Sil. Syst, 676.) 



Fenestella delicata, Meek. 



Plate 10, figs. 2a, b, c, d. 

 Fenestella delicata, Meek (1871) ; Proceed. Acad. Nat. Sci., Philad., XXIII., 159. 



Polyzoum growing in flat flabelliform, very finely reticulated expan- 

 sions ; branches very slender, rigid, bifurcating, and often nearly paral- 

 lel, or gradually diverging, to give room for new ones formed by division ; 

 dissepiments about half as thick as the branches, alternating or oppo- 

 site, and but little expanded at the ends, as seen on the non-poriferous 

 side; fenestrules very uniform, oblong, with length usually about one- 

 third to one-half greater than their breadth ; non-poriferous side rough- 

 ened by little nodes along the branches, rather more closely arranged 

 than the fenestrules; poriferous side with a similar row of little pointed, 

 elevations along a more or less defined mesial ridge of each branch; 

 pores comparatively large, alternating, and numbering two, or occasion- 

 ally three, in each row opposite each fenestrule, and one generally nearly 

 or exactly at one or both ends of each dissepiment. 



Size of entire polyzoum unknown, but it apparently attained a length 

 of three inches or more; number of fenestrules in 0.20 inch, measuring 

 longitudinally, 3; do., measuring transversely, 4. 



As seen on the non-poriferous side, this species closely resembles Prof. 

 McCoy's figure of his F. plebeja, natural size, excepting that it forms a 

 slightly finer network. Under a magnifier, however, it is seen to differ 

 in having a row of little nodes along each branch, and I have not seen 

 any longitudinal striae on its branches, though they probably exist on 

 perfect specimens. The magnified figures of the poriferous side of F. 

 plebeja show still more important differences, its fenestrules being pro- 

 portionally much longer, with four or five pores opposite each side. The 

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