OPALINID CILIATE INFUSORIANS — METCAL.F 



575 



These tropical species are closely alike. It would seem, then, that 

 this group dates from a time when the American and African tropics 

 were connected (Cretaceous, or more likely Jurassic, period). 



Protoopalina, Subgeneric Group VI (Group 8 of Metcalf, 192Sa) (fig. 133) 



P. scaphiopodos Metcalf, in Scaphiopus, a pelobatid, southwestern United 

 States. 



P. hammondii Metcalf, in Scaphiopus, southwestern United States. 



P. mexicana Metcalf, in Scaphiopus, northern Mexico. 



P. mitotica (Metcalf), in Ambystoma, west-central United States. 



Figure 133.— Geographic distribution of Protoopalina, subgeneric group VI. 



This compact, sharply distinct, and highly evolved group of species 

 have dumbbell-shaped nuclei. They doubtless evolved from a pelo- 

 batid parasite, like P. pelohatidis, when the pelobatid host, Scaphiopus, 

 had reached North America during the Tertiary period. In the 

 host genus they spread, east of the mountains, as far south as northern 

 Mexico, and one species turning eastward reached the Atlantic coast. 

 Scaphiopus is a genus of strange habits, burrowmg and seldom seen. 

 Once, in Woods Hole, Mass., where it had been almost unknown, 

 Scaphiopus holhrookii appeared, breeding by the many hundreds in 

 surface pools after a good rain. Perhaps this genus may be secretly 

 present in other regions from which it has not been reported. 

 Protoopalina, Subgeneric Group VII (fig. 1S4) 



P. ovalis Fantham, in Rana, South Africa. 



P. ovoidea Metcalf, in a gastrophrynid, Texas. 



These forms are probably distinct from each other, though they 

 inese iuiiiis u ^ j ^, , • f p o»a/is are much more 



agree in form and dimensions, ine nuciei oi r . wuv 



