222 BRITISH FOSSIL TRIGONI^. 



culated costae ; the plain antecarinal space is always well developed, and is usually the 

 only smooth portion of the shell. The variability assumed by the three species T. gihhosa, 

 T. Damoniana, and T. Manseli, in their surface-ornaments, are so considerable (ex- 

 emplified on our Plates XVIII, XIX, and XXI) as to offer a remarkable contrast to 

 other examples of the GlahrcB, and surpass in diversity, perhaps, any other of the more 

 ornamented examples of the genus. T. gibbosa, more especially, which I have arranged 

 in three varieties, becomes in one of them a shell almost devoid of ornament, and is 

 chiefly remarkable for the prominence of its zonal sulcations ; in other forms its surface 

 is crowded by its excentric costae, and roughened by their small prominent tubercles. 



The Isle of Portland, Tisbury, Warminster, Brill, and Swindon are the localities at 

 which the Trigonice Glabrcs are the predominating forms, the other sectional examples 

 of the genus having altogether disappeared. The European continental Glabra of the 

 same period are T. MichelloUi, De Lor. and Pellat, ' Boulogne,' pi, vii, fig. 6 ; T. 

 variegata, Credner, ' Ob. Jura,' pi. viii, fig. 22, also a variety of the latter from Boulogne 

 figured by De Loriol and Pellat, pi. xi, fig. 9. The latter species has the posteal 

 portions of its costae broken, forming lengthened oblong nodes, unlike the British species 

 which are all tuberculated ; T. Bonlogniensis, De Lor. and Pel. ' Boulogne,' pi. vii, fig. 

 10^ has irregular plicated costae, destitute of tubercles, and has no zonal sulcations. 



Of the seventy-eight species of Jurassic Trigonice, exclusive of varieties, found in 

 Britain, and recorded in this Monograph, twenty-eight are also obtained at various 

 European continental localities, but chiefly in France and Switzerland ; six of these also 

 occur in Southern Germany, and one species {T. iriquetra, Sub.), Plates VI and 

 XXXVI, in Northern Germany. 



The general European assemblage of Jurassic Trigonia contained in the British 

 Museum are so considerable, varied, and abundant, and their state of preservation so excep- 

 tionally fine, that it becomes a subject of regret so small a portion of them should come 

 under the observation of the public ; eventually this defect will be removed and a series 

 of Trigonia disclosed, so remarkable and attractive that it may confidently be predicted 

 they will engage the special attention of future palaeontologists. The prevailing forms 

 belong to the Clavellatce, Undidatce ^ and Costata, only a minority of which can be 

 identified with recorded species. 



Other European Jurassic Trigoniae, not British, figured and described, are : 



Trigonia costata. Chap, et Duv. Foss. de Luxemb., tab. 25, figs. 6, 7. 



— costata, var. triangularis, Goldf. Petref., tab. 137, fig. 3. 



— similis, Ag. Trig., tab. 2, figs. 18 — 21. 



— navis, Lam. Ag. Trig., tab. 1, 2, figs. 21 — 24. 



— costellata, Ag. Trig., tab. 2, figs. 1 — 12. 



— Bronnii, Ag. Trig., tab. 5, fig. 19. 



— maxima, Ag. Trig., tab. 4, figs. 6 — 9. 



— Goifussii, Ag. Trig., p. 31. 



