BRACHIOPODA JACKS* >X 189 



In general form the 'Terr;! Nova " species is ovately triangular, broadest 

 antrriiirly : lairral margins merging into anterior margin without, angulation. The 

 I\|M> n|' folding is dorsallv uniplicate (I'l. I. tigs. :!. ('.). 



I'nitli valves are about equally inflated and perfect lv rounded in carlv stairs, hut 

 lieconie limadly flattened anieriorlv, later in growth. The surface uf Imth is denselv 

 eovered with tine regular hair-like radii. Delicate growth-lines occur at irregular 

 intervals. These are more numerous arid closer ton-ether towards the .-interim- liorder. 

 The radii increase in nunilier l>y intercalation, and apparently extend from the nejiinnic 

 portion, which is semi-elliptical in outline with fine incremental lines. Thev are 

 variable in number in different specimens, and in different situations on the same 

 individual. They are plainly visible through the shell. (hie specimen from 

 Station 194. on microscopic examination revealed nine radii per mm., about the 

 middle of the ventral valve ; ten (possibly eleven) nearer the beak ; and an average 

 of eight near the anterior margin. Other specimens from the same Station and from 

 Station 3 1C yielded somewhat similar results i.e., an average of nine radii per mm. 

 in the middle, and higher numbers posteriorly. The spaces between the radii are 

 unequal, and this accounts for some difference in their nunilier per mm. The mosaic 

 formed by the calcareous prisms of the inner layer of the test is shown in PI. I, fig. 10. 

 This figure also shows two of the radii seen through the shell from the inside. 



The ventral valve is pointed posteriorly, and has a short recurved beak ; the 

 pedicle-opening consists of two parts a small rounded notch, permesothyrid* in 

 position, opening into a wide ovate clelthyrium. bounded anteriorly bv discrete 

 deltidial plates; dental plates vertical, extending from below the slightly recurved 

 teeth backwards into the beak-cavity ; pedicle-collar very distinct, occupying quite 

 half the length of the pedicle-opening (PI. I, fig. 4). The lateral margins of the 

 valve are slightly curved, passing over extremely rounded angles into a rounded 

 anterior margin. The interior of the valve is smooth, with fairly dear traces of the 

 muscular impressions ; these are clustered together in the umboiml region a little in 

 advance of the teeth. The continent adductor scars are in the middle in the form of 

 a heart-shaped mark (a little posterior to the centre of the group), which is almost 

 surrounded by the flabelliform didm-tor impressions; behind the latter and overlapping 

 them slightly are the scars of the ventral peduncular muscles. 



The dorsal valve is roundly pointed posteriorly; the cardinalia consist of two 

 divergent socket-ridges, bounding deep and transversely Amoved dental sockets ; 

 crural bases well marked, extending as ridges obliquely from the apex, and attached 

 to the inner sides of the socket-ridges by means of transversely striated curved 

 lamella-, which are grooved alongside the crural liase ridges: crura short, abruptly 

 truncated, or very slightly denticulated, at the extremities. On their posterior inner 

 sides the crural liases send down strongly curved lamella-, which are fused to a posterior 



* For definition of this term, see Bueknian [1910, p. 131]. 



