BEYOZOA. 288 



Callopora pulchella.l 



The small size of the branches and bushy habit of growth distinguish the species 

 from all the other known Minnesota species of the genus. Externally its zoaria are 

 exceedingly like those of an un described form occurring in the Cincinnati quarries 

 associated with C. dalei Ed. and H. 



Formation and locality.— Yevy abundant in the upper third of the Trenton shales, rare in the Galena 

 shales, at St. Paul and Cannon Falls, Minnesota. 



Mus. Reg. No. 8112. 



Callopora pulohella, n. sp. 



PLATE XXII, FIGS. 1-12. . 



Zoarium dendroid, branches averaging 5 mm. in diameter, tapering slightly, the 

 oldest parts sometimes attaining a diameter of 7 mm., the young extremities only 3 

 or 4 mm. The branches divide dichotomously at average intervals of 12 mm., and 

 never, so far as observed, inosculate. Surface exhibiting small conical monticules, 

 2.0 to 2.5 mm. apart, their summits generally with small aggregations of mesopores. 

 As shown in the figures, the hight of the monticules varies in different examples, and 

 in some they are to be described as rounded rather than conical. Zooecial apertures 

 small, subcircular, enclosed by rather thick, ridge-shaped walls, regularly arranged, 

 subequal, thirteen or fourteen in 3 mm. Mesopores very small and, though numer- 

 ous, often difficult to distinguish externally with an ordinary pocket lens. This 

 difficulty is greatest in old examples in which they are partially filled by calcareous 

 deposits. 



Internal characters: Vertical sections show that in the axial region the prox- 

 imal end of the tubes is crossed by from two to four diaphragms, beyond which these 

 structures are absent till we reach the middle of the comparatively wide peripheral 

 region when each zooecial tube is again intersected by one or two. Mesopores are 

 abundant and closely tabulated. In tangential sections the zooecia are subcircular, 

 their walls somewhat ring-like and in contact with each other in only a limited 

 degree, the interspaces being occupied by more or less numerous mesopores varying 

 considerably in size and shape. Just beneath the surface of a fully matured example 

 the walls are thickened by internal deposit, the mesopores small and approximately 

 of uniform size. At deeper levels the walls are thinner and the mesopores larger and 

 more irregular in shape and size. In transverse sections the axial region is made 

 up of decidedly angular tubes of which those of the larger set are also comparatively 

 small while those of the minor set are less regularly distributed than usual. 



This form is to be compared with the C. dalei Edwards and Haime, of the Cin- 

 cinnati group, from which it differs chiefly in having fewer diaphragms and slightly 



