Brachiopods in the Persian Gulf. 43 
follows:—Shell transverse oval; valves unequal; ventral 
convex and deep, with subdued earination, dorsal flattened 
and shallow, with feeble median sinus on anterior two-thirds 
(i. e., the shell is ventrally uniplicate). The exterior of the 
ventral valve is covered with sparse strize which are some- 
what incipiently aculeate, especially on the lateral parts of 
the valve. Some strizw disappear before reaching the anterior 
border in the middle part. On the lateral parts interpolated 
strie appear towards the margin as discontinuous nodulose 
ribs. ‘There is a distinct cardinal area, which is striated 
transversely. The interior of this valve is almost smooth in 
the umbonal part, becoming nodulose towards the margin. 
The nodules radiate from the posterior end. There is a short 
pedicle-collar joining up with the bases of the teeth, and a 
distinct median septum reaches almost to the middle of the 
valve. The latter extends under the pedicle-collar, but does 
not support it. On the exterior surface of the dorsal valve 
the striz are less in number and of a different character. In 
the umbonal region they are thick and somewhat nodulose. 
Some of these reach the margin as thin striee, others disappear 
entirely or die out for a time and then reappear near thie 
margin. The striz are not so noticeably aculeate as on the 
ventral valve. A slight but distinct area (transversely 
striated) is visible on each side of the median notch. The 
interior of the dorsal valve is strongly nodulose (or papillose), 
the nodules being arranged in rows radiating from the beak. 
The hinge-processes (cardinalia) consist of widely divergent 
dental sockets and socket-ridges (hollowed out underneath). 
There are no median hinge-plates, and the crura arise from 
the anterior corners of short plates attached to the undersides 
of the dental socket brackets. In the umbonal portion 
(between the brackets) is a callous deposit on the floor of the 
valve, from which extends a stout median septum which 
reaches almost halfway down the valve. The brachidium or 
loop is unfortunately slightly imperfect, but is essentially as 
in typical AZ. truncata, with lateral lacunee, as in the latter. 
All the specimens of M/. truncata which [ have seen from 
Mediterranean localities (both recent and fossil) have nume- 
rous thin striz on the surface of both valves, the strice at 
times being distinctly nodulose ; but among a small number 
of specimens from Teneriffe, Canaries (70 fath.), there is one 
which shows an approach to the above-named var. pauci- 
striata. 
With the exception of the sparse and peculiar striation, 
the characters detailed above are seen generally in typical 
