112 PERMIAN FOSSILS. 
It is quite unnecessary at the present day to enter into any details proving the 
distinction between [Hypothyris and Terebratula. Yn addition to what I have elsewhere 
published,’ the subject has been ably elucidated by Mr. Morris ;? and no conchologist, 
I believe, has demurred to the separation. 
Hypothyris appears to have withstood all the changes which organic nature has 
been subject to on our planet; as species have lived and succeeded each other from 
almost the earliest organic period to the present moment. They were most abundant 
during the primary and secondary periods; few are known to have existed during the 
tertiary; and only two species appear to be living at the present time. The one generally 
known, Hypothyris psittacea, has an extensive geographical range in the northern 
hemisphere, having been found in the icy seas of the arctic circle, and on the coast of 
Northumberland.* 
The next genus is now for the first time proposed for a singular group of shells 
which have long been without a proper standing place in our conchological systems. 
Genus Lsorhynchus,’ King. 
Type Terebratulites equirostris, Schlotheim, as represented by De Verneuil in the’ 
‘Géologie de la Russie d’Europe,’ vol. ii, pl. tii, fig. 1. 
Diagnosis.—Sub-globular ; sub-eequivalved; tumid behind, and compressed in 
front ; slightly areated ; generally striated ; and with large punctures. Uwmdéones of nearly 
equal size; that of the large valve foraminated at its apex. Large valve with two long 
de France’ has made typical of the former genus; but this I can say, the name Rhynconella cannot super- 
sede that of Hypothyris for a genus typified by the dtrypa cuboides,—for this reason, that such a genus 
(without going back to the year in which it was provisionally proposed by Professor Phillips, which is not 
allowable in the present case) was defined both by Mr. Morris and myself, and also typified by one of us, 
two years previously to M. A. d’Orbigny’s resuscitating the Waldheimian name RAynconella: In making 
these observations I wish it to be understood, that I shall most cordially agree with what M. A. d’Orbigny has 
done connected with Rhynconella, provided it does not clash with Hypothyris : it is very possible this is the 
case, considering that this author has been describing cretaceous Hypothyride, which have certainly some 
appearance of being generically distinct from the normal species of the Paleeozoic rocks ;—but I am not aware 
of the distinction having yet been established. 
1 Vide Ann. and Mag. of Nat. Hist., vol. xviii, pp. 32-6. 
2 Quarterly Journal of the Geological Society, vol. ii, part i, pp. 382-9. 
3 The other species, named by Mr. G. B. Sowerby, Terebratula nigricans, and described in his beautiful 
‘Thesaurus Conchyliorum,’ has not yet had its locality determined. 
4 Vide Aun. and Mag. of Nat. Hist., vol. xviii, p. 238; and Forbes and Hanley’s ‘ iPratfeth Mollusca,’ 
vol. ii, p. 348. The specimens which I procured on the coast of Northumberland were an entire shell anda 
rostral valve ; the former, which is the original of the figures in the ‘ British Mollusca’ (pl. lvii, figs. 1, 2, 3), 
is now in Mr. J. G. Jeffrey’s rich collection of British shells, and the latter I presented to the Museum of 
the Natural History Society of Northumberland, Durham, and Newcastle-on-Tyne. 
> Etym. ioos, equal; puyxos, a beak—in allusion to the nearly equal size of the umbones. 
