ANIMALS. 133 
area equal to the width of the shell; slowly decreasing in height from the centre to 
the terminations, which are bluntly tapering: swrface covered with regular imbricated 
lamellze of growth, which, in passing over the ribs, appear as if undulating: zzcremental 
lamelle very finely striated in the cross direction, which results from the microscopic 
capillary-like fibres constituting the substance of the shell. Sma// valve two thirds the 
length of the large valve, and similarly ribbed : median elevation moderately prominent : 
area low: umbone slightly prominent: punctures extremely small. 
I strongly suspect that the fossil which de Verneuil has doubtingly identified with 
the Terebratulites hystericus of Schlotheim, and the “ espéce indéterminée” of the same 
author are referrible to the present species. 
Trigonotreta undulata (as well as the last species) is prettily ornamented with 
regular imbricated lamine of growth crossed with fine striae, which, when examined 
with a magnifier, are seen to resemble capillary fibres regularly arranged in parallel 
series, as represented in fig. 17, Pl. IX. 
This species occurs in the compact limestone at Midderidge (Sowerby); in the 
shell limestone at Tunstall Hill, and Humbleton Quarry; and in the Breccia at 
Tynemouth Chiff. It has not yet been noticed in Germany, owing probably to its 
being confounded with Zrigonotreta alata. The ‘‘espece indéterminée, and the so- 
called ‘ Spirifer hystericus Y are from the Permian rocks of Russia; the former from 
Bielebi (government of Orenbourg), and the latter from Kirilof. 
TRIGONOTRETA PERMIANA, King. Plate IX, figs. 18, 19, 20, 21, 22, 23, 24. 
SPrRIFER Permianus, King. Catalogue, pp. 7-8, 1848. 
Diagnosis —Margin “ semi-elliptical. Twice as wide as long. Lateral surfaces with 
four or more sharpish, rather distant ribs. JJesial furrow or ridge not much larger 
than the adjoining folds. Beak erect’* in casts; but gibbous in testiferous specimens. 
Valves marked with regular lamelle of growth, crossed with hair-like strize. 
This well-marked species, which rarely exceeds an inch in width, and half an inch 
in length, differs from Zrzgonotreta undulata in having a narrower median furrow, or 
elevation, and only half the number of folds, which are broader and more angulated 
than those of the latter: the valves are not so tumid, and the lateral extremities 
are rounded instead of pointed. These distinctive characters are equally well dis- 
played on young as on old specimens. The valves are marked with lamelle of 
growth and punctures agreeing with those of the last two species. 
I have seen in Mr. T. Davidson’s collection a Belgian fossil, which, if I mistake 
not, Dr. de Koninck has identified with Zrzgonotreta cristata, Schl.: it has a closer 
resemblance, however, to the present species; but it differs in having large punctures. 
1 King, Catalogue, pp. 7-8. 
