DE. T. DAVIDSON ON KECENT BEACUIOPODA. 



173 



Fig. 19. 



fibrous. Colour liglit yellowish grey. lu the interior of the dorsal valve are two short, 

 curved lamella? for the support of the labial appendages. Length 

 12 lines, breadth 13, depth 7 lines. 



Hnb. Dredged by Dr. L. Doderlein, in about 160 fathoms, in 

 Sagami Bay, Japan. 



Obs. We are indebted to Dr. L. Doderlein for the discovery of 

 this very remarkable recent form of Bhynchonella, and he kindly 

 forwarded for my inspection and description the four examples 

 he procured during liis dredgings in Japanese waters. When 

 young the shell is flattish, neither fold nor sinus being yet de- 

 veloped ; the ribs are also few in numljcr, and the spines have 

 not yet been formed. In external appearance and size it bears 

 some resemblance to the Jurassic Rhynchonella sjjijioaa ; but in 

 this last-named species the spines are very much longer and irre- 

 gularly implanted on the ribs, while in H. Doderleiiil they are 



arranged in rows. 



It is with much pleasure that I name this very interesting 

 species after its discoverer. 



A. Adult It Dbderhini, 



Davidson. 



B. Portion of external 



surface, cnlarj^cd, to 

 show ribs, inter- 

 spaces, concentric 

 lines, and siiines. 



Genus ATRETIA, Gwyn Jetfreys, 1870. 



Type Atretia r/novioii, Gwyn Jeffreys. 



Only two species of this genus have been discovered. The characters of the type, 

 A- gnomon, are fully given in tlie description of the species. 



100. Atretia gnomon, Gwyn Jeffreys. (Plate XXV. figs. 0-13.) 



Cryjttopor a gnomon, Gywn Jeffreys, Nature, vol. i. p. 13G, 1869. 



Atretia gnomon, Gywn Jeffreys, Preliminary Report of the Scientific Exploration of the Deep Sea in 

 H.M.S. Surveying Vessel 'Porcupine,' Proc. Roy. Soc. vol. xviii. p. 421, 18G9; Ann. & Mag. Nat. Hist. 

 4th ser. vol. xviii. p. 251, 187fi, and Proc. Zool. Soc. 1878, ])p. 112, 41.3, pi. xxiii. figs. 4, 4«, 4 6. 



Dimerella gnomon, Dall, Proc. Acail. Nat. Sci. Philadelphia, 1873, p. 197. 



Atretia gnomon, Davidson, Suppl. to the Recent and Tertiary Brachiopoda, Brit. Foss. Hracliiopoda, 

 vol. iv. p. 7, 1874. 



Shell very small, triangularly oval or pear-shaped, widest and rounded anteriorly, 

 tapering posteriorly, somewhat compressed, thin, white, semitransparent. and glossy. 

 Dorsal valve slightly convex, with a shallow longitudinal depression commencing at 

 about half the length of the valve and extendini? to the front. Ventral valve sli"htlv 

 deeper than the dorsal one, with a wide slightly raised mesial fold commencing at about 

 half the length of the valve, and extending to the front ; beak moderately produced, 

 angular at its extremity, moderately incurved, with a triangular incomplete foramen 

 commencing under the extremity of the beak, margined anteriorly by tlu; umbo of the 

 dorsal valve, and laterally l)y narrow rudimentary deltidial plates. Surface smootli, 



23* 



