22 Dey ian ackson—Brachiopod Morphology. 
T. grayi cannot be referred to Magellania, or even to Dallina, on 
account of the ventral valve possessing dental plates in the form of 
strong buttresses with a small recess behind each. Dental plates are 
entirely absent from Magellania throughout life, and also from Dallina 
septigera and D. floridana, so far as the adult stages are concerned, 
but according to Fischer & Oehlert! the teeth of the ventral valve 
in D. septigera are supported in a young state by dental plates. 
These become attenuated with age and disappear entirely in the 
adult. TZ. grayi, therefore, is in need of a new generic name, as it 
cannot be referred to Zerebratalia even, on account of the loop being 
in a higher stage of development. ‘The name Zhomsonia, therefore, is 
now proposed for this form. ; 
Let us now turn to Zerebratalia. This genus was founded by 
Beecher? on Terebratula transversa, G. B. Sowerby, a ventrally 
uniplicate shell, but, as Thomson points out, the actual species on 
which Beecher established a different ontogenetic series from that of 
Terebratella s.str. was Terebratella obsoleta, Dall. 
Thomson considers this latter species to be a dorsally uniplicate 
form, and on this account creates a new genus—Dallinella—tfor its — 
reception. Beecher’s outline drawing of 7. obsoleta* is very misleading, 
and gives a very erroneous idea of the type of folding. Dall’s figure * 
is also of little service as it is only a dorsal view, but his description 
is very clear. I possess a specimen which agrees exactly with Dall’s 
description, and shows the true folding to be undoubtedly ventrally 
biplicate. ‘he anterior margin of the shell has much. the same 
appearance as in some specimens of Magellania flavescens.© The teeth 
of the ventral valve are supported by dental plates which are rather 
more definite than in Zerebratalia transversa and Thomsonia grayt.® 
In the dorsal valve the cardinalia is of the same weak character as 
in the two species just mentioned. The species, therefore, seems to 
me to be rightly placed in the genus Zerebratalia. 
Thomson further suggests that 7. transversa, Sow., and 7’ coreantca, 
Adams & Reeve, are true Zerebratella, and if so Terebratalia becomes 
a synonym of Torebratella. 
T. coreanica agrees with ZT. transversa and Thomsonia grayi in 
having the same type of dental plates and weak cardinalia, except 
that the cardinal process is somewhat more definite. Like Thomsonia 
grayt there is a callous deposit in the umbonal area. This species 
and 7. ¢ransversa cannot, therefore, be separated from the genus 
Terebratalia. 
Such structural features as dental plates are, in my opinion, 
worthy of more consideration than has been given them in the 
identification and description of species. They are not only helpful 
1 Hxpéd. Scient. du ‘‘ Travailleur’’ et du ‘‘ Talisman ’’, 1880-3, Brachio- 
podes, Paris, 1891. 
2 Op. cit., p. 382. 
3 Op. cit., pl. ii, figs. 6-9. 
4 Proc. U.S. Nat. Mus., xvii, pp. 726-7, pl. xxx, fig. 7, 1895. 
5 See Davidson, op. cit., pl. vii, figs. 6b, 10. 
6 The dental plates in both these are very similar, and appear to have been 
overlooked in descriptions of the species. 
