182 DE. T. DAVIDSON ON EECENT BEACHIOPODA. 



n, lateral gastro-parietal band ; o, centi'al ditto ; pp, ilio-parietal bands ; q, heart ; ?•, brancbio- 

 systemic vein ; s, aorta ; tt, dorsal and ventral, pallial or genital arteries ; n, right ventral 

 oviduct; !<*, portion of left ditto cut through, v, oesophageal ganglia; w, sheath of crural 

 process or oral lamina; x, orifice leading into ditto; y, portion of ditto of the opposite side; 

 z, terminal sac of the left great brachial canal ; z*, ditto of the right or opposite arm, seen 

 through the mesenteric membrane." 



Kg. 10. Portion of shell of Rhynchonella psittacea (after Carpenter), showing at aa the internal surface, 

 with the imbricated arrangement of the extremities of the component prisms, and at b the 

 aspect of the prismatic substance, as displayed by a fracture nearly in the dii'cction of the 

 length of the prisms, showing also the entire absence of the least trace of perforations ; mag- 

 nified 100 diameters. 11. Portion of the shell-sui-face of the same (after Carpenter), more 

 highly magnified, showing the imbricated arrangement and the entire absence of perforations. 



Figs. 12-13 c. Rhynchonella psittacea, var. Woodivardi, A. Adams. From Japanese waters. (Both in 

 the Davidson Collection, Geol. Dept., British Museum.) 



Figs. 14-15 b. Rhynchonella lucida, Gould. From Japanese waters (Davidson Collection, Geol. Dept., 

 British Museum). 15, 15 a, 15 6 enlarged. 



Figs. 16-19. Rhynchonella nigricans, Sowerby. A series of specimens from Faveau Strait, New Zealand. 

 (Davidson Collection, Geol. Dept., British Museum.) 



Fig. 20. Rhynchonella nigricans, var. pyxidata, Boog Watson. From off Kerguelen Island, ' Challenger ' 

 Expedition. (Zool. Dept., British Museum.) 



Plate XXV. 



Figs. 1, 1 c. R/njiichonella Grayi, S. P. Woodward. 1 c. Enlarged. Habitat not quite certain. 

 (Zool. Dept., British Museum.) 



Figs. 2-4. Rhynchonella cornea, Fischer, MS. Dredged off Cape St. Vincent, 'Talisman' Expedition 

 (Mus(3um d'Histoire Naturelle, Paris). 3. Obtained by Dr. Gwyn Jefl'reys, chops of the English 

 channel (Dr. Gwyn Jeffreys's Collection, now in Boston Museum, U. S. A.). 4. Portion of the 

 interior of the dorsal valve, enlarged, to show the hinge-plate, curved lamellie, and muscular 

 interior impressions. 



Fig. 5. Rhynchonella sicula, Seguenza. Fossil in the Pliocene limestone of Messina, and supposed by 

 Dr. Gwyn Jcfireys to occur in the recent condition. 



Figs. G-13. Atretia gnomon, Gwyn Jeffreys. 6, 7. Natural size. 7, 8 a. Enlarged. Dredged by Dr. 

 Gwyn Jefl'reys during the Norwegian Arctic Expedition, about thirty miles west of Tromso, on 

 slopes of the banks. 9. Dredged by Herman Friele off the coast of Finmarken, about thirty 

 miles west of Tromso. 10. Interior of the dorsal valve of a specimen dredged by the ' Talisman ' 

 Expedition off Morocco (Marquis de Folin's Collection). 10 a. Showing the largely 

 developed mesial septum. 11 and 13. The dorsal valve, from specimens dredged by Dr. Gwyn 

 Jeffreys. 12. Fragment of the interior of the ventral valve, to show the developed dental plates. 



Figs. 14, 15. Rhynchonella Dciderleini, Davidson, ]\IS. From Sagami Bay, Japan. In the collection of 

 Dr. Doderlein. 



Figs. 16-17 a. Atretia Brazieri, Davidson, MS. Dredged by Mr. John Brazier ofl^ Port Stephens, New 

 South Wales. 17. Intei'ior of dorsal valve. (Davidson Collection, Geol. Dept., British Museum.) 



Tretenterata. 



Figs. 18-23. Discina striata, Schumacher, sp. 18. A typical specimen, after Sowerby. 19,19 a. A 

 malformation. 20, 20 a. An enormously thickened upper valve. 21. Interior of the same 

 valve, luuch enlarged (Davidson Collection, Geol. Dept., British Museum). 22, 22b. Type of 

 Discina Evansi, Davidson; from Bodegas (Cuming Collection, Zool. Dept., British Museum). 

 23, 24. Type of Gould's Crania radiosa, from Cape Palmas (National Museum, Washington, 

 D.C.). 25. Exterior of the upper valve, much enlarged. 25. Exterior of the lower or foraminated 

 valve. 24. Interior of the same valve, much enlarged. 26. Section of the valve, to show 

 the position of the foramen. 



