BRYOZOA—CRYPTOSTOMATA. 153 



118. A. armatum Ulrich. (Fig. 205, /.) Ordovicic. 

 Of three sets of joints, secondary and tertiary more slender 



than primary which have sharply-defined articulating sockets, and 

 small apertures in six ranges with strong spines near each ; sec- 

 ondary segments with apertures in five or six ranges between 

 strong ridges, and with lower lip spiniform. 

 Trenton of Minnesota, etc. 



119. A. billingsi Ulrich. (Fig. 205, k.) Ordovicic. 

 Primary segments 3.5 to 4 mm. long, each with two secondary 



segments (4 mm. long) upon each side (4 in all), the succeeding 

 ones 2 mm. long ; apertures subquadrate, 6 in 2 mm. 

 Trenton of Canada. 



LXVIII. Nematopora Ulrich. 

 Slender, ramose, with pointed basal extremity, not jointed ; sub- 

 tubular zocecia arranged radially around one or two minute axial 

 tubes, with oval or subcircular apertures, and peristomes generally 

 in linear series between longitudinal ridges. Ord.-Dev. 



120. N. ovalis Ulrich. (Fig. 208, a.) Ordovicic. 

 Bifurcating at intervals of 2 mm., diameter 0.3 to 0.4 mm. ; large 



oval apertures, peristomes connected by short ridges, in four or 

 five ranges. 



Trenton of New York, Canada, and Minnesota. 



LXIX. Rhombopora Meek. 

 Slender, non-articulate, and solid branches; apertures in longi- 

 tudinally or diagonally intersecting series; rhombic or diagonal 

 vestibules, in the region of which the zocecia are thick walled ; 

 acanthopores sometimes of two types, large and small. Sil- 

 Carb. 



121. R. tenuirama Ulrich. (Fig. 208, b.) Mississippian. 

 Branches 0.4 to 0.5 mm. in diameter; apertures oval, between 



slightly flexuous longitudinal ridges, carrying both large and small 

 spines. 



Chester of Illinois and Kentucky. 



122. R. lepidodendroides Meek. Carbonic. 

 Average diameter of branches 1.75 mm., largest 3 mm. ; zocecia 



in regular quincunx order, oval, with rhombic vestibules, margined 

 by a single or double row of spiniform tubuli, with a large spine 

 at the angle. 



