272 DR. C. T. TREC1LMAXX ON THE [vol. lxxiX, 



Oxytoma sp. (PI. XII, figs. 6 & 7.) 



Description. — The beak of the left valve is situated about the 

 anterior fourth of the hinge-line, and projects very slightly above 

 it ; the hinge-line is straight, the posterior wing is sharply 

 prolonged, the anterior wing does not project beyond the lower 

 anterior margin of the shell. The posterior margin is hollowed 

 out below the wing, the lower margin is rounded. Four strong 

 sharp raised ridges diverge from the beak and pass to the margins, 

 one to the middle of the posterior margin, another, the strongest, 

 to the lower margin beyond which it is prolonged into a finger- 

 like process, and the other two, slightly curved, to the anterior 

 margin. Between the main ribs the surface of the shell is 

 decorated with very numerous close-set radial ribs ; on the anterior 

 and posterior portion of the shell these are all very even and 

 small, but on the median part some of them are rather larger 

 and more prominent than the rest. Growth-furrows occur at' 

 irregular intervals. The right valve is rounded in outline, consider- 

 ably smaller than the left, and is nearly flat. It has a small and 

 slightly raised beak Avhich does not project above the hinge-line, 

 and in front of it there is a small rounded anterior auricle with an 

 angular indentation below it. The radial ribs correspond with 

 those of the left valve, but are faintly marked and do not seem to 

 be prolonged much beyond the margin of the valve. 



Dimension s. — Left valve : length =21 mm. ; height= 21 mm. 

 Right valve : length and height=about 13 mm. 



Locality. — Junction of Ta^ylor's Creek and the Otapiri; Psilo- 

 ceras Beds. An impression of a left valve from which a gutta- 

 percha scpieeze was made is illustrated in fig. 6. Another specimen 

 consists of a left valve partly broken away, showing the right 

 valve in position (fig. 7). 



Remarks. — The left valve bears a close resemblance to the 

 3'oung portion of a specimen of O. cygnipes Young & Bird from 

 the Middle Lias of Market Harborough (Leicestershire). I 

 hesitate, however, to identify it with this Avell-known species, 

 because of its occurrence in New Zealand with ammonites of the 

 lowest Lias, and because in one of the New Zealand specimens the 

 right valve is much smaller than the left ; whereas, in the above- 

 mentioned English form, the right valve seems to be aboiit equal 

 in area to the left, and to have similarly prolonged ribs. 



Oxttoma sp. (PI. XII, fig. S.) 



Description. — The beak is anteriorly situated, and is well 

 differentiated from the rest of the shell. It is narrow and 

 inflated, and projects slightly above the straight hinge-line. 

 There is a blunt rather flat posterior wing, with a slight marginal 

 excavation below it. The lower posterior margin is slightly pro- 

 duced, the lower margin gently rounded and somewhat produced, 

 the anterior margin gently rounded, and there is a small anterior 

 wing. The inflated beak merges gradually into the surface of the 



