234 Mr. J. Lycett on some new species of Trigonia 



divisional sulcus, which passes parallel to the median row of 

 tubercles upon the area. The clavellated portion of the shell 

 has a very numerous series of rows of concentric tubercles ; the 

 tubercles are small near to the marginal carina, and become 

 larger towards the middle of the curvature ; they are distinct, 

 rounded, closely arranged (15 or 16 being contained in a row), 

 the number of rows being about twenty, the whole of which are 

 distinctly tuberculated ; the lines of growth upon the sides of the 

 shell are fine and distinct. The dimensions are equal to the 

 largest examples of the clavellated TrigonicB. 



This elegant shell is nearly allied to T. perlata, Ag., which is 

 an Oxford clay species ; in that shell however the umbones are 

 more recurved, the carina have much larger tubercles, and the 

 median carina has in addition a series of transverse varices which 

 are absent in T. decorata. It has sometimes been mistaken for 

 T. clavellata, but differs from that well-known form in the fol- 

 lowing particulars. 



The Inferior Oolite shell is less elongated, the umbones are 

 not recurved, the posterior border is not concave, the general 

 figure has less convexity, the area is more flattened, and the lan- 

 ceolate space is much smaller and not striated; the rows of 

 costse are more numerous ; the tubercles are more numerous, 

 more closely arranged and less prominent. Another large cla- 

 vellated species, the T. muricata, Goldf., approaches more nearly 

 to the figure of our shell, but the Portuguese species has the area 

 much more narrow, the costse are less numerous, but much more 

 elevated, the tubercles being larger and more distantly arranged. 



The figure likewise closely agrees with T. Bronnii, Ag., from 

 the Terraine k Chailles or Oxford clay ; but the ornamentation of 

 our species, both upon the area and the sides of the shell, is more 

 minute and delicate, with more numerous rows of costse, the 

 carinse having no distinct elevation as in the species of Agassiz. 



Trigonia decorata occurs abundantly in the Trigonia grit 

 throughout the Cotteswolds, but the test is very fragile, and is 

 difficult to detach from the hard matrix. Rodborough Hill near 

 Stroud has produced it in great numbers. 



Trigonia gemmata, Lycett, n. sp. PI. XI. fig. 8. 



Shell small, ovately trigonal, excavated and somewhat rostrated 

 posteriorly, rounded anteriorly ; umbones obtuse, somewhat re- 

 curved, surface moderately convex; area narrow, transversely 

 striated and bounded on each side by a narrow, elevated and 

 striated carina, which is also gracefully curled ; costa? numerous, 

 closely arranged, elevated, acute ; the ui)per third of the valves 

 has concentrically curved and finely tuberculated costse, those 



