210 DE. C. T. TRECHMANN ON [vol. Ixxiii^ 



It occurs fixed to the surface of other shells, but seems to have a 

 partiality for attaching itself to the large Nautilids. The free 

 or upper valve reproduces the sculpture of the shell to which it is 

 attached. The lower sessile valve is verj thin, and is closely 

 attached by the whole of its surface. The crura diverge at about 

 a right angle, and the margin of the valve is marked by a row of 

 fine radiating furrows. The free or left valve is convex, and the 

 growth-lines are irregularly spaced and well marked. The hinge- 

 line is straight, and occupies almost the greatest wddth of the 

 shell ; but the area is obscure or absent. 



Locality and horizon. — Bed c, Otamita, Hokonui Hills, 

 Carnic. Prof. P. Marshall collected a large crushed Gri/poceras, 

 which had a great part of its surface covered Avith these shells. 



Myopiioria nuggetexsis, sp. nov. (PI. XXII, fig. 10.) 



The shell is sub-triangular in outline. The beaks are situated 

 slightl}^ forward of the median line, are pointed, close together, and 

 turned very slightly but perceptibly backwards. 



The anterior margin is rounded, the posterior lower margin some- 

 what prolonged and angular. The keel, which passes from the 

 beaks to the lower posterior margin, is prominent, and the two parts 

 of the shell separated by it make a i-ather sharp angle one with 

 the other. The groove in front of and adjoining the keel is very 

 slightly wider, but no deeper, than the other radial grooves, and 

 a line of very small nodes passes down the middle of it. About 

 eight ridges, broken by the growth-lines into nodes, pass from the 

 beaks to the lower and anterior margin. Behind the keel the 

 shell is almost flat, and is covered with fine growth-lines and 

 small irregular pimples, which vary in size. A shallow furrow 

 passes down the middle of the flat posterior portion. The posterior 

 muscle-scar is suboval and deep on the side nearest the beak, but 

 shallower towards its lower margin. The pallial impression is well 

 marked. 



The left valve has one very strong central triangular tooth, not 

 perceptibly divided, but strongly grooved on both sides, eight 

 grooves on the posterior and six on the anterior side ; there is a very 

 feeble anterior tooth, strongly grooved on its inner side, and a very 

 thin posterior tooth scarcely differentiated from the shell-margin, 

 not grooved. Length = 08 mm. ; height = 47 mm. 



Locality and horizon. — About ten specimens, from which 

 the above diagnosis was drawn up, were obtained from a bed at 

 Nugget Point, known to New Zealand geologists as the ^ Trigonia'' 

 Bed. It comprises about 15 feet of a very hard fine-grained 

 greywacke rather low in the Carnic, about 700 feet below the 

 Mytilus-iwohlemniicus Bed, and immediately above a thick bed of 

 granitic conglomerate. The shells occur somewhat plentifully as 

 single valves, or often with the two valves open or slightly dis- 

 placed. They are difficult to collect, owing to the hardness of the 

 rock ; but, by preparation of the material and dissolution of the 

 shell, satisfactory gutta-percha impressions were obtained. 



