198 SUPPLEMENT TO THE BBITISH 



185. Rhynchonella tetraedra, Sow. Dav., Ool. Mon., p. 93, PI. XVIII, figs. 5, 9 



(not 10, which belongs to R. sub -decor ata), 

 PI. XVI, figs. 13, 14; Sup., PI. XXIX, 

 fig. 6. 



Rhynchonella lacunosa, Dav. (not of Schlotheim). Ool. Mon., p. 96, pi. xvi, 



figs. 13, 14, 1852. 



I have very little to add to my description of this very abundant and variable species, 

 further than to correct a mistake I made at p. 96 of my Oolitic Monograph, in referring two 

 specimens of Rh. tetraedra to Rhynch. lacunosa, Schl. The two specimens in question 

 had been sent to me by the late A. Robertson, of Elgin, as having been procured from the 

 Oxford Clay of Dunrobin. Subsequently, Prof. Judd, having visited the locality, found 

 that these specimens had come from near the top of the Lower Lias (Zone of Am. 

 oxynotus, Lias /3 of Quenstedt), in rocks north-east of Dunrobin Castle, Sutherland- 

 shire, and that it had been found in the same zone, near the village of Tobermory, 

 in the Island of Mull (H. Miller). In England it is quoted by Professor R. Tate from 

 the three upper divisions of the Middle Lias, or Zones oi Am. capricornus, A.margaritatus, 

 and A. spinatus. It is a common fossil in the Middle Lias or Marlstone of Straithes, 

 near Whitby, in Yorkshire, and in most of the Liassic localities where the zones above 

 mentioned occur. 



In the ' Yorkshire Lias,' p. 421, Prof. Tate expresses the opinion that Quenstedt has 

 figured a series of medium-sized, and young examples of Rh. tetraedra under the name of 

 R. amalthei ('Die Brachiopoden/ pi. xxvii, figs. 154 — 160); but I am not convinced 

 that such is the case, as will be found recorded in my description of Rh. amalthei. 

 Professor Tate states that in Rh. tetraedra the beak in the young is sub-erect, not 

 incurved, as in the adult ; that the shape is depressed and sub-triangular, and that in the 

 youngest forms traces of the plaits are discernible. Pie adds that Simpson considers his 

 Rh. compressa as probably another variety of Rh. tetraedra, but that he has not seen 

 specimens on which the species is founded. Professor Tate also observes that the 

 species occurs in Yorkshire, in the zone of Am. armatus at Robin Hood's Bay, in that 

 of Am. Jamesoni at Huntcliff, Coatham, Peak, in the Am. margaritatus Zone at Danby 

 Dall, Carlton Moor, Huntcliff, in the Am. spinatus Zone in the Cleveland Main Seam, 

 where it is abundant ; also at Eston, Upleatham, &c, and Straithes, Grosmont, Millington. 

 It also occurs in the Marlstone of Leicestershire ; the young specimens are nearly flat. 



It is very variable in shape, and perhaps the following varieties might deserve to be 

 distinguished. 



