PLATE IV. 



MUECHISONIA SERRULATA (page 20). 



(Not serrata, as in page 20.) 



Figure 1. Murchisonia serrulata. Natural size; 1*, a portion magnified. 



MURCHISONIA HELICTERES (page 21). 



" 2. Murchisonia helicteres. A normal specimen. 



" 3, 3a, 4. . The same species, irregularly uncoiled. The 



sutural edge on the uncoiled whorl is indicated at s. 



Murchisonia bicincta (page 19). 



" 5, 6. Murchisonia bicincta, Hall. Ordinary large variety. 



" ?. — ! — , — Variety with more angular whorls, and 



without the upper keel. (Var. perangulata, Hall.) 



