320 PROCEEDINGS OF THE ACADEMY OF [1879. 



11. OPHIOCRINUS Angelin. 

 1878. Iconogr. Crin. Suec, p. 24. 



Ill the form and structure of the calyx this type resembles 

 Cyathocrinus, but in the position of the arms it is like Arachno- 

 crinus, from which it is perhaps only subgenerically distinct. 



Underbasals five, four of medium size, equal, thin, upper edges 

 meeting at right angles, except the fifth is truncated above. Radials 

 five, lunulate ; articulating surface deeply concave, and occupying 

 almost the entire width of the plate. Brachials spreading out 

 horizontally, varying in number from one to four in the different 

 rays ; very short but heavy. Only one anal plate. 



Arms directed downward; composed of joints similar to the 

 brachials, being, however, slightly narrower and longer. Total 

 length of arms unknown. 0. crotalurus had apparently only ten 

 arms ; in the original specimen some eight or nine arm joints are 

 preserved without any signs of bifurcation. The arm grooves are 

 rather narrow, covered by two rows of plates ; with short lateral 

 grooves given off from each side of the main furrow, within the 

 arm joints, similarly covered, and which are evidently recumbent 

 pinnulae. 



The condition of the ventral sac is the most remarkable feature 

 of the genus. Instead of going straight upward, it bends close 

 to the base, and coils upon itself spiral^ twice, decreasing in 

 thickness toward the upper end. It is composed of regular rows 

 of hexagonal plates alternately arranged, with a rather deep 

 lonoitudinal ridsje bordered with fissures on each side. 



Column round, of alternate larger and smaller joints ; central 

 perforation of medium size. 



This genus resembles Cyathocrinus, but is easily distinguished 

 by its peculiar pendent arms, recumbent pinnulae, and remarkable 

 proboscis. 



Geological position, etc. Upper Silurian. Sweden. 



The ox\\y known species is 



1878. Ophioerinus crotalurus Angelin. Iconogr. Crin. Suec, p. 24, pi. 4, figs. 8 

 a-c. Upper Silur. Gotland, Sweden. 



12. BOTRYOCRINUS Angelin. 

 1878. Iconogr. Crin. Suec, p. 24. 



