EOMESODON. 57 



Description of Purbec/cian Specimen- -The type specimen (Text-fig - . 22) was 

 obtained by the late Mr. F. .1. Barnes, F.G-.S., from the roach bed of the Portland 

 Stone at Portland. The occurrence of the species in the Purbeck Beds is 

 uncertain, but an imperfect specimen in the British Museum seems to agree with 

 it in the parts which are comparable. 'Phis fossil (PI. XIII, fig. 1), which is not 

 much more than half as large as the type, is of approximately similar proportions, 

 but lacks entirely the upper part of the head, the paired fins, and the caudal fin. 

 The external hones and scales are ornamented with very prominent large hollow 

 tubercles. The orbit is relatively large, and the cleft of the mouth small; and 

 some of the lateral vomerine teeth are crimped round the shallow apical pit. As 

 shown in broken section the bones are of very open texture. The typical rather 

 stout neural and haemal arches of the axial skeleton, with traces of their laminar 

 expansions, are seen in the caudal region. The fragmentary dorsal and anal fins 

 have clearly about 30 and 20 supports respectively, while all the rays are very 

 .stout, closely articulated, and subdivided distally. Some of the anterior rays of 

 the anal fin are armed with rows of very small and slender, slightly arched 

 denticles (fig. 1 c, a.). The scpiamation on the large and deep abdominal region is 

 shown chiefly in impression, but a few actual remains of scales above the position 

 of the notochord bear traces of the canal for the lateral line. The number of 

 •complete transverse series of scales cannot have been less than 20 ; and the scales, 

 being less deepened, seem to have been more numerous in each series than in the 

 typical Mesodon. Fragments of the dorsal ridge-scales bear very stout large 

 smooth denticles (figs. 1 a, 1 b), and the ventral ridge-scales have these denticles 

 still larger, each of the scales just in front of the anal fin bearing only one denticle 

 with a boss in front (fig. 1 c). 



Horizon* iiml Localities. — Portland Stone (Roach Bed) : Isle of Portland. 

 (?) Middle Purbeck Beds : Swanage, Dorset. 



2. Eomesodon depressus, sp. nov. Plate XIII, fig. 2. 



Type. — Fragment of head and trunk ; British Museum. 



Specific Characters. — Elevation of back steep in front, but gradually descending 

 to the rather remote dorsal fin; most of the dorsal ridge-scales bearing eight small 

 denticles which are nearly uniform in size. 



Description <>( Specimen. — Though well distinguished by the characters of the 

 dorsal ridge, this species is known only by the fragmentary type specimen 

 (PI. XIII, fig. 2) which was discovered by the late Mr. Frederick Hovenden, F.G.S. 

 The orbit (orb.) and the postorbital part of the skull are vaguely indicated, and 

 the steep anterior profile of the fish does not appear to have been distorted. The 

 very coarse tuberculation is visible on the fragments of head-bones preserved. 



