MOLLUSCOIDEA. 321 



Genus IDMONEA Lamark. 



Idmonea abbotti Gabb & Horn. 



Plate XXII., Figs. 3-4. 



1860. Heterocrisina Abbottii G. & H., Jour. Acad. Nat. Sci. 



Phil., 2d ser., vol. -4, p. 404, pi. 69, figs. 45-47. 

 1862. Bicrisina\ Abbotii G. & H., Jour. Acal. Nat. Sci. Phil., 2d 



ser., vol. 5, p. 174, pi. 21, fig. 65. 

 1864. Bicrisina Abbottii Meek, Check List Inv. Foss, N. A., 



Cret. and Jur., p. 4. 



1868. Bicrisina- Abbottii Con., Cook's Geol. N. J., p. 723. 

 1905. Bicrisina abbotii Johns., Proc. Acad. Nat. Sci. Phil., 



1905, P- 5- 



Description. Zoarium small, composed of laterally com- 

 pressed, more or less subtriangular bifurcating branches, .5 mm. 

 or less in thickness. Zocecia arranged in transverse or somewhat 

 oblique rows upon two sides of the branches only, each row con- 

 taining three or four zocecia, the most anterior one in each row 

 being the larger; the rows of zocecia on the two opposite sides 

 usually alternate in position. The apertures when perfect are 

 circular, with an elevated rim, and are directed forwards or out- 

 wards. Surface of the zoarium between the rows of zooecia, 

 excavated, concave, smooth. Posterior surface of the branches 

 reticulately marked, the longitudinal lines being the most con- 

 spicuous. 



Remarks. This species is one of the commoner forms in the 

 Vincentown fauna. It is very closely related to /. communis 

 d'Orb., from the Upper Cretaceous of France, and it is possible 

 that the two forms should not be considered as distinct. 



Formation and locality. Vincentown limesand, Vincentown 

 (154), near Mullica Hill (Gabb and Horn). 



Geographic distribution. New Jersey. 



21 PAI, 



