BRYOZOA. 561 







short, depressed, about half as wide as the branches. Fenes- 

 trules long-oval, small, about 0.3 by 0.1 mm., and eighteen or 

 nineteen in 1 cm. Zoopcia in two ranges, twenty-three or twenty- 

 four in 5 mm., with small, widely separated, circular apertures, 

 and elevated peristome. 



On the reverse the branches and dissepiments are on the same 

 plane, usually ridge-shaped, forming quadrangular fenestrules of 

 greater width than on the opposite face. On mature examples 

 the branches are smooth or very finely granular. On young 

 ones they are faintly striated. 



This species is very common in the Warsaw beds, and occurs 

 also, but rarely, in the Keokuk group. It is closely allied to 

 the Keokuk H. plumosa (Fenestella plumosa Prout,) but differs 

 in having nine or ten fenestrules in 5 mm., while that species 

 has only 6.5 to 7.5 in the same space. There are most proba- 

 bly other differences, but the Keokuk species has not been ob- 

 served in a sufficiently good state of preservation to permit of 

 comparisons in the minute details of structure. As usual Prout's 

 types of H. plumosa were denuded of the superficial net-work. 



Below are described two varieties of H. proutana. 



Position and locality: Rare in the Keokuk group at Warsaw, 

 111., and Keokuk, Iowa; abundant in the Warsaw beds at War- 

 saw, and Monroe Co. in Illinois, and less common at Barrett's 

 Station, St. Louis Co., Mo. The species occurs also in the St. 

 Louis limestone of Caldwell Co., Ky. 



HEMITRYPA PROUTAXA var. VERMIFERA n. var. 



PL LVn, Fig. 5-5a. 



This variety is represented by a number of specimens which 

 agree closely in their proportions with typical H. proutana. 

 The following differences have been noticed. The branches and 

 dissepiments on their reverse side are rounded instead of angu- 

 lar, and the fenestrules are more oval. The principal feature, 

 however, are certain peculiar, tubular, vermiform bodies, which 

 are irregularly distributed over and form part of the reverse 

 face of the zoarkim. They are about 2 mm. long and 0.5 mm. 

 in diameter, lie more or less nearly parallel with the branches, 

 70 



