CLAVELLATA. 19 



tuberculated varices ; the posteal extremities of the rows approach the carina at an angle 

 which is somewhat greater than a right angle ; the tubercles in the rows are large, not 

 prominent, imperfectly rounded, closely arranged, and are rather unequal both in size and 

 figure ; eight tubercles are usually distinct in each row before they degenerate anteally 

 into small varices ; the last-formed one or two rows in specimens of advanced growth have 

 the tubercles compressed into lamellar varices, or form almost continuous costse. ' The 

 shell in the Lower Calcareous Grit, which I regard as the type, has sixteen or seventeen 

 rows of costae in adult specimens ; this form is special to the Lower Calcareous Grit and is 

 the prevailing clavellated species of that rock both in Dorsetshire and Yorkshire. A clavel- 

 lated Trigonia special to the Kimmeridge Clay, and very much resembling the typical T. 

 clavellata of the Lower Calcareous Grit will, without due care, be placed with the latter 

 species. For a comparison of these forms see the species next following. 



Of the mistakes in the identification of species T. clavellata is a remarkable instance, 

 the errors respecting it having been chiefly those of Continental authors, who have not had 

 the advantage of comparing authentic English specimens, and have been misled or con- 

 fused by the figure of Parkinson, which unfortunately has priority ; this drawing is in 

 every respect execrably bad, and undeserving of trust, so that after many unsatisfactory 

 attempts at comparison with English Trigonias I have felt compelled to discard it 

 altogether, and to regard the figure in the ' Mineral Conchology' as the typical example, as 

 it is altogether free from doubt, and is readily identified with numerous Weymouth 

 examples obtained in the Coralline Oolite formation or Lower Calcareous Grit of that 

 vicinity. Nevertheless, this variety admits of some variability of figure, and we may 

 regret that one or two additional specimens were not figured in the ' Mineral Conchology ;' 

 as an instance, refer to the figure in Mr. Damon's supplement to his ' Geology of Wey- 

 mouth,' which accurately represents a specimen of abnormal form, with the anterior side 

 very short, and the tubercles in the rows so large as to be partially confluent. Upon the 

 whole, the larger figure of Goldfuss (' Petr.,' pi. 136, fig. b, c) is the best hitherto given of 

 the adult form, but the locality (Inferior Oolite of Gundershofen) is unquestionably an 

 error. 



The T. clavellata, Agassiz, from the Oxford Clay of Dives, is remarkable for the great 

 elevation and recurvature of the umbones, and the horizontal direction of the rows of 

 costse. D'Orbigny has justly separated this species under the name of T. major ; it has 

 not been recognized in Britain. 



The T. clavellata of Zeithen is so very unlike the English species that we may be 

 confident no true example of T. clavellata had come under his notice; it appears to 

 coincide with T. sic/nata, Ag. The T. clavellata figured by M. Hebert, from the Oxford 

 Clay of Tronville, is also a different species, remarkable for the great breadth of the area, 

 together with the shortness and prominence of the escutcheon. The Trigonia Bronnii, 

 Ag., of which a single defective specimen was figured in the memoir by that author, has 

 since been fully illustrated and described by M. Hebert in an interesting paper on the 



