1863.] MACDONALD THECIDITJM ADAMSI. 517 



The Government Surveyors publish their papers in the * Natuur- 

 kundig Tijdschrift voor Nederlandsch Indie/ and at present they 

 only map what is actually seen. They are now engaged, under my 

 direction, in surveying the Island of Banka. 



4. Description of a new fossil Thecidium (Thecidium Adamsi) from 

 the Miocene Beds of Malta. By J. Denis Macdonald, Esq., 

 F.K.S., Surgeon of H.M.S. « Icarus.' 



Amongst the many interesting fossils occurring in the lower part of 

 the calcareous sandstone of Malta, there is a beautiful little Theci- 

 dium ; and as I believe it has not yet been described or named, it 

 may be worthy of a brief notice. 



It appears to me that the nearest ally to the little Shell which I 

 am about to describe is the recent Thecidium Mediterraneum. The 

 species about to be described is, however, very much smaller, being 

 only -Lth of an inch in length ; besides which many other decidedly 

 specific differences present themselves on closer inspection. As to 

 its general figure, it much resembles a horse's hoof in miniature, the 

 fixed ventral valve corresponding to the unguis or body, the hinge- 

 area to the soft posterior part of the " frog," and the dorsal valve 

 to a shoe-plate. This comparison gives a good idea of the obliquity 

 of the shell in the longitudinal plane, the great depth of the ventral 

 valve, and its lengthened surface of attachment (figs. 1-3). 



The dorsal valve (fig. 1, b) measures rather more transversely than 

 longitudinally. The hinge-line is straight, but interrupted in the 

 middle by a small subquadrate cardinal process (fig. 3, a), fronted 

 above by a depressed but very distinct umbo, and below by a deep 

 excavation (b) receiving a trifid process (fig. 2, b) of the ventral valve 

 for the attachment of the adductor muscles. From the hinge -line 

 forwards the margin of the dorsal valve (fig. 3) is rounded, but it is 

 slightly cut off or sinuated in front. It is, moreover, as a character 

 of the genus, minutely granulated inferiorly (cZ). The tooth (c) on 

 either side of the base of the cardinal process (a) is rather small, 

 and received into a corresponding dental socket in the opposite valve. 



The internal calcareous framework, is very complex in appearance, 

 consisting of the following parts, namely : — first, an outer simple 

 loop (fig. 3, e) following the contour of the shell, but lying a little 

 within the granulated margin ; 2ndly, two half-loops or hook-like 

 processes (fig. 3, /) included by the former, and turning inwards and 

 forwards posteriorly ; and 3rdly, an inner perfect loop (fig. 3, g), with 

 the free central portion, or bight, reflected downwards and forwards, 

 and giving off from its concavity a median crest (h), which projects 

 backwards, and is flanked on either side by the inverted hook-like 

 ends of the intermediate half-loops. The attached surface of all the 

 parts just mentioned is very considerable, and the simple and reflected 

 portions of the inner loop are connected by a more or less perfect 

 calcareous expansion. 



Just below the hinge, and connected with the ventral valve, there 



