BBYOZOA. 405 



DESCRIPTIONS OF SPECIES. 



PROTOCRISINA Ulrich. 



(For generic diagnosis see page 369). 



PROTOCRISIXA EXIGTJA Ulrich.* 



PI. XXIX, flg. 4-4c, and PL T.TTT, fig. n-iie. 



Zoarium ramose; branches slender 0.6 mm. wide, 0.3 to 0.45 

 mm. thick, dividing dichotomously at a very acute angle afc in- 

 tervals varying from two to seven mm. Celluliferous side 

 strongly convex, smooth, with four, occasionally only three, 

 series of zooecia. Reverse faintly convex, flattened or slightly 

 concave in the central part, finely striate, the striae often 

 minutely granulose. Zooecia subtubular, thin-walled within, with 

 prominent tubular mouths. Apertures subcircular, 0.09 mm. in 

 diameter, five or five and one-half in two mm. vertically: ar- 

 ranged in oblique rows. A small number of circular pores, 0.04 

 mm. in diameter are scattered over both the reverse and cellu- 

 liferous faces. 



Position and locality*. This species is rare at Wilmington, 

 111., where it is associated with typical Cincinnati group fossils. 

 It is more common and in a better state of preservation in 

 Trenton group strata at Montreal, Canada, and Trenton Falls, 

 X. Y. 



This form can scarcely be regarded as more than a variety of a rather common 

 Trenton group species, in New York and Canada, where it is generally identified with 

 the form to which Hall applied the name of Gorgonia ? perantiqua (Pal. N. Y., vol. I,). 

 This identification is probably erroneous since neither the figures nor the description 

 agree with the specimens. These consist of numerous rigid, remotely bifurcating 

 branches, which are spread upon a plane about their own width apart, with four rows 

 of pores. 4 Hall says the branches are "lax" and carry two laterally opening rows of 

 cells. Under these circumstances it seems to me better to propose a new name for the 

 species than to perpetuate what is obviously an error. 



