D. M. S. Watson — A New Genus of Brachiopods. 213 



specimens of the remarkable Brachiopod which forms the subject of 

 this paper. These specimens are in general perfectly preserved, and 

 are. easily freed from their surrounding clay" by washing with a tooth- 

 brush. 



All the specimens preserved are ventral valves. Each is adherent 

 by the whole of its external surface usually to the outer, but some- 

 times to the visceral surface of the nautilus shell, or even to an 

 adherent Stromatoporoid. Where an individual has been fixed 071 

 a flat surface and has had so much free space round it that it could 

 grow freely, it forms an almost circular area whose margins are 

 exceedingly thin and tightly adherent to the base. On rough surfaces 

 and where two individuals have met and interfered with one another 

 the general form may be very irregular. The largest individual 

 I have measures 2'4 X 1"7 cm., the smallest "75 X "65 cm. 



The hinge-line is straight and very short, in adults one-sixth the 

 width of the shell. It is a very distinct groove whose posterior side 

 is formed by a ridge standing up from the shell. The posterior 

 surface of this ridge falls rapidly to an expansion of the valve which 

 is usually of small extent, and in the smallest individual is nearly 

 absent. The posterior surface of this ridge is the area, so reduced as 

 to be almost unrecognizable. The delthyrium is represented by an 

 extremely shallow notch in the middle of the hinge-ridge, which is 

 invariably present though difficult to see. There is no trace of 

 a deltidium either true or false. 



On the anterior side of the hinge-line and at its outer ends are two 

 triangular thickenings separated from one another by the posterior 

 end of the cavity of the valve. These thickenings presumably 

 represent the teeth, although as they do not project at all and cannot 

 have been interlocked with anything in the dorsal valve it may be 

 more accurate to regard them as the remains of dental plates. I shall 

 refer to them as the dental areas. Each dental area is shallowly 

 concave antero-posteriorly and in young examples is obscurely striated, 

 the strise running parallel to the median plane of the shell. At its 

 antero-lateral corner each dental area passes directly into a thickening 

 of the shell which runs round to meet the other in the middle line 

 anteriorly. This thickening, which forms a very definite flange rising 

 from the generally flat visceral surface of the valve, is thrown into 

 loops, symmetrically disposed and pointing towards the cardinal 

 region. In the youngest individual the only well-marked loop is 

 axial in position, passing from the anterior margin more than half- 

 way to the hinge-line. In older specimens this axial loop becomes 

 much enlarged and may reach three-quarters of the distance from the 

 anterior margin to the beak. In all the specimens except the youngest 

 there are in addition two main pairs of loops symmetrically placed; 

 of these the posterior is the larger. Einally there are other smaller 

 emarginations which in still more aged individuals might be supposed 

 to become loops. In certain specimens the outer parts of the loops 

 may become confluent, forming a single ridge. 



The flange is always highest at the inner end of a loop and 

 shallower peripherally. The flange is sharp-margined, and, except 

 in the loops, excavated on the inner side just below its edge so as to 



