244. PERMIAN FOSSILS. 
Thamniscus dubius, p. 44. 
This fossil and the followmg were found in a fragment of magnesian limestone, brought up, by a 
fisherman’s line, from the bottom of the Coral-zone trough, between the Dogger-bank and the coast of 
Northumberland, about 30 miles from the latter. The circumstance is noticed here, as it may assist, with 
other facts, in throwing some light on the geology of this submarine region. 
1. Thamniscus dubius. 6. Epithyris elongata. 
2. Archeocidaris Verneuiliana. 7. Pecten pusillus. 
3. Cyathocrinus ramosus. 8. Monotis speluncaria. 
4. Cythere elongata. 9. Bakevellia ceratophaga. 
5. Trigonotreta multiplicata. 10. Turbo helicinus. 
Palliobranchiata (Histology of), pp. 91, 110, 117, 124. 
The reader is referred to some observations by Vicomte d’Archiac, on the nature of the shell-tissue of 
this class of Mollusks, in the ‘Mém. Soc. Geol. de France,’ 2me s., tome ii, part ii; as I am anxious that 
he be in possession of all that has been published on this still-imperfectly understood subject. 
Palliobranchiata (Classification of), p. 81, &e. 
Some facts, which have lately come to my knowledge, induce me to make a few slight modifications in 
some of the Ancylobrachial families and: genera. 
Leaving untouched the two families Thecideide and Argiopide, I am led to think, that the genera 
included in the families Terebratulide and Rhynchoride, ought to be arranged according to the character of 
their apophysary system. I am not quite acquainted with the principles of M. d’Orbigny’s classification ; it 
is, therefore, possible, that he may have anticipated me in some of the following views. Guided by the 
beautiful figures which Mr. T. Davidson has from time to time published of the interiors of certain Ancylo- 
brachial genera,—particularly in a late number (June) of the ‘ Annals and Magazine of Natural History,’— 
there is every reason for believing, that two principal forms of the apophysary system generally prevail ;—one 
in which the loop is simply attached by its posterior parts to the crural processes ; and another, in which it 
is attached both posteriorly to the crura, and anteriorly to the medio-longitudinal plate. Waldheima 
Australis affords a good illustration of the first form; and Terebratella Chilensis of the second. By con- 
sidering these forms of the loop, as of fundamental importance in classification, we certainly bring together, 
in the same group, genera, which, in their external characters, differ widely from each other ;—as Megerlia 
and Terebratella,—the former with an area, and the latter without one; Waldheimia and Delthyridea (? D. 
pulchella Tereb. id.‘ Nilson), which stand in precisely the same relation to each other. But Iam strongly 
1 T regret not having been able to obtain any information respecting the apophysary system of 
Terebratula pectiniformis, which appears to be the type of M‘Coy’s genus Delthyridea. 1s there any generic 
relation between this species and Nilson’s Terebratula pulchella? Mr. Davidson has published a beautiful 
figure of the interior of the latter shell. Externally, both have a striking resemblance to each other ; and it 
is further established, by Teredratula pulchella having, as Mr. Davidson informs me, the apex of the umbone 
truncated with a foramen. The next point for inquiry is,—does the loop of Tereératula pectiniformis agree 
with that of T'erebratula pulchella in having a single attachment; if so, the latter will have to be placed in 
the genus Delthyridea, and stationed in the family Terebratulide. 
