27 
towards tlie middle. The surfaee of each of these valves is ornamented with 
from twelve to eighteen radiating ribs, separated from one another by furrows 
of equal size and crossed by concentric growth striations. 
Observation. — I have followed the examj)le of my learned friend, Mr. 
T. Davidson, in keeping, provisionally, this species under the genus Atrypa, 
until its characters should have been better defined. Mr. J. Hall is of 
opinion that it should come under his genus LeptocccUa} 
Horizon and Localities. — This sj)ecies is characteristic of the upper 
beds of the Llandovery ; it is rarer in the lower beds. It is very common in 
some localities, and is found in England, Scotland, Ireland, and America. In 
Australia it occurs at Duntroon. 
Genus — EETZIA, King. 
Hetzia Salteei, Davidson. 
Terebratula Douchardii, Davidson, 1848, Bull. Soc. Geol. France, Y. (2), p. 332, pi. 3, 
fig. 33. 
Terebratula Salieri, Idem, 1848, Ibid., V, p. 331, pi. 3, fig. 31. 
Letzia Loiicliardii, Salter, 1859, in Murchison’s Siluria, p. 250, fig. 4. 
,, Salteri, var. ? Loucliardii, Davidson, 1871, Mon. Brit. Sil. Brach , p. 127, pi. 12, 
fig. 26 and 28-30. 
This shell could be easily taken for a HhynGhonella, if one had not the 
presence of its sjiires for guidance. It is usually oval, a little longer than 
broad. The valves are almbst equally arched. Their surface is ornamented 
Avith tAventy-one to twenty-nine small folds or radiating ribs, rather angular, 
of these the two or four median ones of the dorsal valve are a little thinner 
and less elevated than the others ; the ventral valve is provided with a large 
sinus, the bottom of which contains one or three ribs thinner than the others. 
The entire surface is traversed by equidistant concentric lines of growth, and 
is covered, when .the specimen is in a good state of preservation, by very 
small spines. The specimens entrusted to me agree exactly with the descrip- 
tion and figures given by Mr. T. Davidson. One of them has its spires 
preserved ; it is identical with Eigure 27a. 
Horizon and Localities. — This species is rare in the Wenlock limestone 
of Dudley, but fairly abundant in that of Pi,ock Farm, Longhope. It is fairly 
common in a brownish-grey limestone at Yarralumla. 
E 
^ See Davidson, Mon., p. 107 [137]. 
