S80 CEETACEOUS PELECTPODA 



specimimbus, costulis et striis radiantihus crispatis seu undalatis et in elevatione 

 diagonali angulatis ornata, in adultis costulce radiantes scepe plus minusve ohsoletcB, 

 sed stricB incrementi multo distinctiores sunt, Cardo denticulo obtuso in utraque valva 

 infra umbones sito instructus. 



Sliell elongately ovate, slightly arcuate, with terminal depressed beaks, and a 

 very narrow anterior end, the posterior and dorsal portion is greatly dilatated and 

 becomes gradually very flattened, the ventral side is comparatively narrow, preci- 

 pitous, and slightly incurved at the margin, a shallow depression running as usually 

 from the beaks to the median part of the ventral margin. The hinge has in each 

 valve a distinct obtuse cardinal tooth below the beak, the one in the right valve 

 being a little more remote from the beak than that in the left one. 



Young shells when well preserved (see fig. 6, enlarged three times,) have the 

 entire surface covered with more or less undulating radiating ribs, those on the ventral 

 slope being thinner than others ; they are on the median convexity of the shell 

 angularly bent. When the surface of the shell is not well preserved, as is often 

 the case in older specimens, the ribs gradually disappear, with the exception of 

 those on the ventral slope, but the concentric strise of growth become instead 

 much more distinct (see fig. 7). 



The present species belongs to the type of Modiola Guerangeri, d'Orb., but 

 is readily distinguished from it by the more flattened and expanded dorsal portion 

 of the shell. Among recent forms I may quote M, vexillum, Reeve, from Aus- 

 tralia. These species represent a small group of striated Modiolce, for which the 

 name BracJiydontes may be sub-generically reserved ; they have no striae at the 

 lower anterior end. In another small group represented by the next fossil species, 

 the striae are developed on the anterior and posterior end of the shell, while they 

 become obsolete on the ante-median ventral depression. In this latter group also 

 the striae or ribs are usually not angularly bent along the diagonal elevation of 

 tlie shell, resembling in this respect striated Mytili, 



Locality, — Neighbourhood of ComarapoUiam, in a light coloured sandstone. 



Formation, — Arrialoor group. 



6. Modiola annectans, StoUczha, PI. XXIII, Pigs. 8-9. 



Mod. testa elongata, paulo arcuata, angusta^ tumida^ non carinata ; margine 

 dorsali fere uniforme lente curvato, ventrali ante medium insinuato, antice angus- 

 tissima, posfice angustatim sui-rotundata ; umbonibus anticis, lente incurvis, depres- 

 siusculis ; superficie costellis continuis, tenuibus, radiantibus, in depressione ventrali 

 obsoletiSy striis incrementi subtilissimis et confertissimis decussatis ornata, 



I have already noticed that this species belongs to a small group, represented 

 in a fossil and recent state. The radiating ribs are very fine and decussate by 

 minute striae of growth. The former become obsolete on the ventral depression 

 and are again strongly marked on the anterior end, which is only slightly developed 



