164 
MR. W. K. PARKER OX THE STRUCTURE AND 
8. The processes of the basal plate are all very slender, and there is a pair of small 
extra-hyals. 
9. The squamosals have a very narrow supra-temporal part, and the vomers are of 
great size, especially their dentigerous lobe. 
Second genus. Acris. 
44. (A) Acris Pickeringii. —Adult female; 10 lines (f inch) long. Cambridge, 
Mass., U.S. 
Although essentially a Hylodes, this minute Frog is worthy to be put into a sub¬ 
genus ; I therefore retain for it the term Acris . The skull of this species is very 
valuable as showing the effect of dwarfing in a remarkable arrest of the chondro- 
cranium, such as is seen in the dwarfs of other genera, in different and distant 
regions. The small species of Rappia from Australia, e.g. R. bicolor, and similar 
minute Oxydactyle Frogs from the same territory, e.g. Camanolius, have the same 
modification of their skull— almost all toindows, with but narrow strips of wall ; and 
this is also seen, but to a less extent, in the small Bombinator Toads of Australia, viz.: 
Pseudophryne. Hence it is evident that this economy of cartilage is due to the same 
cause as the general arrest in size of these species. On the other hand, some of the 
smallest kinds are most ossified, notably a species close akin to this, and to Rappia 
bicolor, viz.: the small Rappia from Lagos; and some of the small edentulous Anura 
show the same thing, e.g., Hylaplesia —a Platyclactyle type : the smallest of the typical 
Frogs, Rana pygmoea, has also a very bony skull. 
This skull (Plate 30, figs. 1-5) has its breadth slightly greater (one-twentyfifth) than 
its length ; it is semi-oval in its facial outline, has a broad but rounded muzzle, and 
its quadrate condyles (q.c.) end opposite the middle of the columella. 
The occipital condyles ( oc.c .) are large, reniform, and postero-inferior; they are 
separated by a space nearly equal to the width of both, and this wide notch is 
crescentic. 
There is a wide basal or median tract of cartilage, in which the remnant of the 
notochord is seen to be enclosed in a feeble bony sheath—a cephalostyle—the rudiment 
of a basioccipital ( b.o .). Above the wide foramen magnum {fan.) the roof-cartilage 
comes well back, and is seen to be partly calcified, showing the rudiment of a supra- 
occipital bone. This roof is complete up to the same transverse line as that from 
which the optic nerves (II.) emerge ; from thence the roof is membranous nearly up to 
the septum nasi (s.n.). This is the large ovoiclal fontanelle (fo.) ; it is two-fifths the 
length of the skull, and three-fourths the width of the interorbital region. The 
ossification of the hind skull is feeble, and by the two pah's of normal centres ( pr.o., e.o.). 
The ex-occipitals (e.o.) flank the posterior canals (p.s.c.) above, and surround the 
twin nerve-passages (IX., X.) below; the prootics (p>r.o.) climb over the ampullae of 
the anterior and horizontal canals (a.s.c., li.s.c.) above, and half surround the foramina 
