22 Tate — List of Irish Liassic Fossils. 



24. Ceromya gibbosa, Etheridge, Quart. Jour. Geol. Soc, Vol. xx., p. 112, 

 %s. 3-4 (1863). 

 Isocardia Elea, D'Orbigny, Prodromus, Vol. 1., p. 218 (1850). 



'•' Shell ventricose, deep, especially at the umbonal region. Umbones small, 

 sub-central, slightly curved or involute, leaving a wide and exposed lunular 

 region, strongly marked by concentric ridges of growth. Anterior side pro- 

 duced, rounded and gaping. Posterior side attenuated, slightly truncate. 

 Ventral margin much produced, giving the shell a nearly circular appearance. 

 Height, 1 7 inch; depth, 1 - 3 inch ; length, 21 inches." — Etheridge. 



The specific identity of C. gibbosa, Etheridge, with Isocardia Elea, d'Orbigny, 

 results from a comparison of the type specimens ; the diagnosis of the latter is 

 so imperfect as to claim no consideration from palaeontologists. It is as follows : 

 — " Grosse espece bombee, triangulaire lisse, a crochets contournes." 



Geological Position. — Zone of "A. angulatus," Island Magee, Co. 

 Antrim; not rare (Gray, Tate); Cotham, Bristol ! (Napier); "A. Bucklandi" 

 Zone, Lyme Regis ! (Coll. Geol. Soc.) ; Lower Lias, Langres, Haute-Marne ! 

 (D'Orbigny.) 



25. THRACIA jEQUATA, nov. spec. 



Shell transversely oval, ventricose ; umbones medial, obtuse ; hinge line 

 angulated ; anterior extremity rounded ; posterior extremity moderately ob- 

 liquely truncated ; a very faint keel proceeds from the umbo to the postero- 

 ventral margin, ornamented with furrows and close set fine s tri ae , coincident 

 with the ventral margin, which is arched. Breadth, '55 inch ; length, 4. inch; 

 thickness, "25 inch. 



It has much the shape of T. lata, Minister, from which it is distinguished 

 especially by its ventricosity and curved front margin. 



The genus Thracia has not yet been catalogued from English strata, 

 older than the Inferior Oolite, and, indeed, if Myacites mactroides, Schlo- 

 theim, of the Lias, be not a Thracia, then the genus has till now been 

 unknown below the Middle Lias. T. rugosa, Dunker, a Lower Lias shell, 

 is considered to be a Pleuromya, and has been re-described as such under 

 the name of P. Dunkeri, by Terquem, so that T. a>quata is, at the present 

 time, the oldest British example, if not the oldest-known species of the 

 genus. I take this opportunity to announce the discovery, by Mr. E. 

 Welford, of T. glabra, Agassiz, in the Upper Lias Clay at Eydon, where it 

 was found associated with Leda ovum, Inoceramus dubius, and other species, 

 which serve to fix its stratigraphical position in the Zone of "Ammonites 

 communis. " 



Geological Position. — Zone of " A. angulatus, " Waterloo, Larne. Speci. 

 men unique. (P. T. ) 



26. Anatina myacina, nov. spec. Plate I. fig. 16. 



Shell oblong, elliptical, umbones sub-central, small, ventricose, recurved 



