DE. T. DAVIDSON ON EECENT BRACHIOPODA. ISl 



of veiitial valve. 3i. Interior of both valves, showiuj;- the muscles and labial appendages ; 

 from a specimen dredged by K. Forbes iii the Mediterranean. 

 Figs. 35—36. Cistella Barrettiana, Davidson, sp. 35. Exterior of shell of natural size. 35 a. Enlarged. 

 3fi. Interior of dorsal valve, enlarged. Dredged by Lucas liarrctt on the N.E. coast of 

 Jamaica. (In the Cambridge ^luseum.) 



Plate XXIII. 



Figs. 1, 2. Cistella Barrettiana, Davidson, sp. This is the type of Dali's Cistella rubrutiiicta, from Tortugas 

 (National ^Museum, Washington, D.C.). I a. Enlarged. 2. Longitudinal section, to show the 

 large submarginal septum on the dorsal valve. 



Figs. 3, -i. Cistella Schruiiiini, Crosse, sp. 3. After Crosse's figures, enlarged. 4 is an enlarged drawiri" 

 of fig. 3 6. 



Figs. 5, 6. Cistella Ititea, Dall. 5 a. Enlarged. 6. Longitudinal view of the dorsal valve, to show the 

 elevated grooved submarginal septum. From Tortugas. (National Museum, Washington, D.C.) 



Figs, r, 8«. CistelU aittillarum, CvQssCjSi^. 7. After Crosse. 8«. Drawn by myself and cular"ed, alter 

 Crosse's figure. From Guadeloupe. (Crosse's Collection.) 



iMgs. 9-11. Theeidiuiii Barretli, S. P. Woodward, sp. Dredged by Lucas Barrett, north-east coast of 

 Jamaica. 9. E.xterior of shell. 9 a. Enlarged. 10. Interior of ventral valve, enlarged. 11, 

 Interior of dorsal valve, enlarged. (In the Cambridge Museum). 



Figs. 12-22. Thecidiu?nmediierraneum,li\>iso,sp. 12. Natui'al size. 12 a, 0. Enlarged. 13. Shell with 

 both valves open. 14. Interior of ventral valve much enhu-ged, after E. Deslongchamps, showin"- 

 the pailial apparatus in its integrity, of which only a small portion has been removed to show 

 the cavity wherein are lodged the sinuses and the organs of reproduction. 15. Interior of ventral 

 valve of Thecidium mediterraneum, to show the position of the ventral adjuster muscles (a) 

 of the small concave plates, " coques " [h) of Lacaze-Duthiers, to which the extremities of the 

 adductor muscles (Hancock's occlusors) are attached ; and the oval scars (c) left by the divaricator 

 muscles of Ilani-ock (the " muscles abducteiirs " of Lacaze-Duthiers). 16. Interior of dorsal 

 valve, much enlarged : a, c, e,f, and y, ascending process ; h, bridge-shaped process ; i, k, half- 

 crescent or descending process; m, cardinal jjrocess; w, .scar formed by Hancock's adjustor 

 muscles ( = the ''muscles adducteurs lateraux on externes " of Lacaze-Duthiers). 17. Interior 

 of dorsal valve (after Lacaze-Duthiers), to show the labial appendages, much enlarged. 

 18. The Icast-advanecd embryo hitherto examined; it resembles an agglomeration of small 

 cells. 19. Two embryos, a little more developed and suspended from cirri. 20. An embryo 

 with four lobes. 21. An embryo still more developed, enlarged. 22. Median portion of a 

 galling fenude Thceidium, showing the embryo-pouch partly broken, and the posterior median 

 ciri'i at the nioulli, cacli bearing a bundle of embryos. (Figs. 17-22 after Lacaze-Duthiers.) 



Plate XX iV. 



Figs. 1-11. li/iyiirhonella psiftacea, GmvYni, sp. 1. A large example dredged by McAiidrcw and Barrett 

 in Norwegian seas. 2. Dredged near Baffin's Bay by Gwyn Jeffreys during the 'Valorous' 

 Arctic lOxpedition, 1875. 3. Dredged by Capt. Naresat Franklin Pierce Bay, 1875, lat. 70" 25' 

 N., in 15 fathoms. 4, 5. Young specimens from Sitka, dredged by Dall. (All in the Davidson 

 Collection, Geol. Dept., British Museum.) 6. Interior of dorsal valve. 7. Interior of ventral 

 valve. 8. Profile view of same. 



Fig. 9. General side view of the viscera of Rhynchonella psiltacea, after Hancock's figure (Phil. 

 Trans, vol. cxlviii, pi. Ixi. fig. 2, 1858) : — "a, anterior wall of perivisceral chamber; bb, brachial 

 organs ; e, ventral terminations of occlusor muscles ; c* t*, dorsal terminations of anterioi' and 

 posterior occlusors ; r/(/, divaricators, the left one cut through; r/*, ventral « all of perivisceral 

 chamber; e, ])cduiicle; e*, capsule of ditto; /, peduncular muscle; ff, one of the dorsal 

 adjusters; h, one of the ventral ditto; i, oesophagus; J, stomach, exhibiting the two openings 

 of the left hepatic ducts, the liver having been removed from this side ; k, right lobes of the 

 liver; k*, posterior lobe; /i**, anterior ditto; /, dorsal mesenteric membrane; ///;/(, ventral ditto; 



