16 IOWA STUDIES IN NATURAL HISTORY 



eomb confined to the tip of the proximal 

 pinnules, and of the usual type; no carina- 

 tion of the earlier brachials; none of the 

 segments of P, elongated 



Microcomntula 



c2 no comb-like structures on the proximal pinnules 



di there are no deposits in the ventral perisome of the pinnules 

 visible to the naked eye 



el each cirrus socket is bordered proximally and laterally by 

 a prominent raised rim; a narrow circlet of basals sep- 

 arates the centrodorsal from the radials; centrodorsal 

 conical, the cirrus sockets arranged in ten equidistant 

 columns; first syzygial pair and following brachials very 

 obliquely wedge-shaped or triangular 



Atelecrinus 



e2 no raised rim about the proximal and lateral portions of 

 the cirrus sockets; no basals; first syzygial pair oblong; 

 following brachials oblong or slightly wedge-shaped, 

 later becoming triangular, or at least more obliquely 

 wedge-shaped 



fi centrodorsal elongate, conical or columnar, with the 

 cirrus sockets arranged in 10 definite columns 

 gi the ten columns of cirrus sockets are closely 

 crowded on a conical centrodorsal; size small; 

 color yellow 



Adelometra 



g2 the ten columns of cirrus sockets are segregated 

 in five radial pairs separated by high inter- 

 radial ridges; centrodorsal columnar; size me- 

 dium or large; color red or purple 



Zenometra 



f2 cirrus sockets closely crowded, and without definite 

 arrangement 



gi proximal pinnules absent; lowest pinnule on the 

 fifth brachial 



Hypalometra 



g2 proximal pinnules present; the second and fol- 

 lowing brachials bear pinnules 

 hi first pinnule extraordinarily flexible, com- 

 posed of more than 30 segments which are 

 about as long as broad with their corners 

 cut away, appearing like a string of minute 

 beads; second and following pinnules of the 



