DISCINID^. 331 



? Chelodes, Davidson, King, IST^. 



Distr. — TJ. Silurian; Gotland, Sweden. G. Bergma'n^ D. 

 and King. 



Notwitlistanding remarkable points of resemblance, it is our 

 opinion that it is not a palliobranch ; on the contrary, ^\e are 

 strougl}^ inclined to the belief that it belongs to a section of the 

 coelenterates, represented by Calceola and Gonicphj'Uum. — 

 Davidson and King. 



Possibly a coral. Looks like the internal fulcrum of Zirphfea 

 (Leuconyx, H. Adams). — Dall. 



Ltngulops, Hall, 1871. 



Distr.— 1j. Silur. ; N. Am. L. Whitfieldi, Hall. 



Founded upon a cast of the interior of a single valve of a 

 Lingula-shaped shell, but differing from that genus in its inte- 

 rior impressions. The most striking features are : first, a 

 posterior, semicircular, broad zone, with an inner sinused bor- 

 der ; second, ail arched fillet situated below the hinge and on 

 the zone, the crescent characterizing the Trimerellids ; third, 

 a central space marked with scars (the apophysary system ); fourth, 

 linear impressions occurring in the anterior half of the fossil 

 median plate, and pair of primary vessels belonging to the 

 brachioccele. 



Family DISCINID^. 



Shell attached by a pedicel, passing through a foramen in the 

 ventral valve ; valves not articulated ; minutely punctate. 



Animal with a highly vascular mantle, fringed with long, 

 horny setse ; oral arms curved backwards, returning upon them- 

 selves, and ending in small spires directed downwards, towards 

 the ventral valve. 



DisciNA, Lamarck, 1819. 



Sy??. — Orbicula, Sby. (not Cuvier), 1830. Schizotreta, 

 Kutorga, 1848. 



Distr. — 10 sp. West Africa, W. Indies, Malacca, Peru and 

 Panama. Fossil, 64 sp. Silurian — ; Europe, United States, 

 Falkland Islands. D. striata, Schum. 



Shell orbicular, horny ; upper valve limpet-like, smooth or 

 concentrically lamellose, apex behind the centre ; lower valve 

 flat or conical, with a sunk and perforated disk on the posterior 

 side, from which interiorly extends a furrow ; interior polished 



Animal transparent; mantle-lobes distinct all round; labial 

 folds united, not extensile ; alimentary canal simple, bent upon 

 itself ventrally, and terminating between the mantle-lobes on 

 the right side. There are four distinct adductor muscles, as in 

 Crania; and three pair of adjuster muscles for keeping the 



