I)E. T. DAA'IDSON 0,\ EECE^"T BEACHIOPODA. 155 



very Avidc, rudimentary, obtusely anyular lissurc represents the foramen, on each side of 

 which are two very narrow rudimentary deltidial plates. Shell irregularly concentrically 

 striated, Avith numerous small asperities rising- Irom its surface. Shell perforated hy 

 canals visible under feeble magnifying-power. Length 3 lines, breadth 5 lines. Valves 

 articulating by means of teeth and sockets. Interior of the dorsal valve not com- 

 pletely known. Short cylindrical processes project into the interior of the shell from a 

 little under each angle of the wide semicircular foramen, and from about the middle 

 of the bottom of the valve arises a thickened pillar-shaped process or septum, curved 

 towards the hinge, and forked at its extremity. 



Rah. Found attached to large specimens of CaryophylUa ramosa from the coral-fisheries 

 near Tunis, and at other places in the Mediterranean (E. Deslongchamps and Fischer) ; 

 it was also dredged hy the Marquis de Folin at Cap Breton (Landes) in 25-70 fathoms. 



OIjs. In exterior aspect this spegies quite resembles an Anomia. It is the largest form 

 of the genus 'Platijdia with which we are at present acquainted. It was well described 

 in 1855 by M. E. Deslongchamps, and subsequently with greater detail by Dr. Paul Fischer 

 in two memoirs already referred to. In his paper, M, E. Deslongchamps says : — The 

 dorsal valve is at times very irregular, owing chiefly to the shortness of the peduncle. 

 From a superficial examination of the animal in a dried condition my father and 

 myself were enabled to convince oui-selves that the labial appendages seem connected 

 with the apophysary system hy a kind of very delicate network, reminding one of the 

 descending apparatus in TheckUum, which in some species is formed in its upper portion 

 by a calcareous network freely suspended above the visceral cavity. 



In his memoir on JPlutijdia, published in the ' Journal de Conchyliologie,' vol. xii. 

 p. 160, 1872, Dr. Paul Fischer describes and figures some good examples of Pluti/dla 

 Davidsoni dredged hy the Marquis de Folin from tlie Fosse du Cap Breton, which I have 

 also been able to examine through the liberality of the Marquis. In another paper, 

 issued in the Actes Soc. Linn. Bordeaux, t. xxix. 1874, Dr. P. Fischer says (p. 171) : — 

 The brachial apparatus is supported by a little calcareous forked pillar rising from 

 the middle of the dorsal valve. . . . The forked pillar is proportionally much longer 

 than in individuals of similar dimensions of IlegevUa tnmcatu. Mecjerlia tnmcata can 

 be so modified that the valves become moulded on their substratum ; this is occasioned 

 by the shortness of the peduncle, and therefore the peduncular aperture is found almost 

 completely transferred to the dorsal valve — a malformation raised to the rank of a 

 species by the name of J/<?i^er^i« mo«s^r«o«a, Scacchi ; but even in this case we recognize 

 the characters of the species at all ages, and at no stage do Ave find the rudimentary 

 apophysis of Flatydia Bacldsoni. Dr. Fischer proceeds [1. c.) : — The general arrangement 

 of the brachial appendage, in P. Duindsoni, is extremely simple. On each side of the 

 mouth proceeds a horizontal portion, which afterwards bends and forms an incurvature 

 (boucle). It is continued on each side by the running portion directed from tlu^ 

 beak of the valve towards the frontal margin, and connected with the dorsal valve ; 

 this part (portion currente) bends, describes a complete circle, and returns above the 

 running portion, being in relation to the dorsal valve ; it ends at last l)y a sinuosity 



SECOND SERIES. — ZOOLOGY, VOL. IV. 21 



