214 PERMIAN FOSSILS. 



Thamniscus dubius, p. 44. 



This fossil and the following 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. 



2. Arckceocidaris Verneuiliana. 



3. Cyathocrinus rdmosus. 



4. Cy there elongata. 



5. Ti'igonotreta multipUcata. 



6. Epithyris elongata. 



7. Pecten pusillus. 



8. Monotis speluncaria. 



9. Bakevellia ceratophaga. 

 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 * M6m. 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, &c. 



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 Thecidceidce and Argiopida, I am led to think, that the genera 

 included in the families Terebratulidce and Rhynchoridce, 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. Waldheimia 

 Australis aff'ords 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 Delthyridcea (? D. 

 pulchella Tereb. id.^ Nilson), which stand in precisely the same relation to each other. But I am strongly 



1 I regret not having been able to obtain any information respecting the apophysary system of 

 Terebratulapectiniformis, which appears to be the type of M'Coy's genus Delthyridcea. Is 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 Terebratula 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 Terebratula pectiniformis agree 

 with that of Terebratula pulchella in having a single attachment ; if so, the latter will have to be placed in 

 the genus Delthyridcea, and stationed in the family Terebratulidce. 



