LOWER SILURIAN. 



191 



the name, from the Latin malum, an apple), and having no arms, and the ambulacral 

 grooves irregularly radiating; another species is the Palceocystites tenuiradiatus B. 

 (Hall's Actinocrinus tenuiradiatus), which is common, and lias been detected in the 

 granular limestone of West Rutland (Am. Jour. Sci., III. iv. 133.) 



3. Mollusks. — (a.) Bryozoans. — Fig. 306 represents the Retepora incepta H., a 

 thin, reticulate coral, the surface of which, magnified, is shown in Fig. 306 a; Fig. 307, 



Figs. 304-316. 

 307^ ^ 306, 



Radiates. — Fig. 304, Palaeocrinus srriatus ; 305, Malocystis Murchisoni. Mollusks. —3%. Rete- 

 pora incepta ; 307, Ptilodictya fenestrata ; 308, Orthis costalis : 309. Leptaena plicifera ; 310, 

 Rhynchonella plena: 311, Maclurea magna; 312, M. Logani (X%); 313, operculum of same ; 

 314, ScaMtes angulatus ; 315, BeHerophon rotundatus. Articulates. —316, Leperditia Canaden- 

 sis, var. nana. 



Ptilodictya fenestrata H., a small branching species, covered with minute cells, and Fig. 

 307 n, the surface magnified. 



(b.) Bracniopods. — ¥\g. 308, Orthis costalis H. ; Fig. 309, Leptama plicifera H. ; L. 

 incmssata PL; Fig. 310, Eh ynchonelh plena H. (a side-view), a very common species, it 

 almost constituting some beds of the limestone. There are also several Lingulellae [L. 

 Lyelli B., L. Huronensis B.. etc.): Orthis imperator B., a species nearly 1| in. across, be- 

 sides several other species of the genus. 



(c.) Lamelltbranchs. — Vanuxemia Montr ealensis B., a species nearly 1| in. long, re- 

 lated to Avicula. 



(d.) Gasteropoda. — Fig. 311, Maclurea magna, which is very abundant,and sometimes 

 has a diameter of eight inches; Fig. 312, Maclurea Logani, showing the shell closed by 

 its operculum: Fig. 313, the operculum, inside-view; Fig. 314, Scdites angulatus Con.; 

 Fig. 315, Bellrrophon i Burrrnia) rotundatus H. ; Pleurotomaria Calyx B., near Montreal. 



(e.) Cephalnpnds — Orthoceras recti-annulatum H ; O. temmeptum H., a large species, 

 with the septa thin and rather crowded; O. velox B., Montreal, Mingan Ids.; O. dif 

 fidens B., Mingan Ids. 



4. Articulates. — (a.) Trilobites. — Among the species there are Illcenus Arcturus 



