N0.1177. NORTH AMERICAN LEPTONACEA— BALL. 891 



A. 23. This, upon careful comparison, proves not to be quite the 

 same as Montacnta tumiduhi Jeffreys.^ Au examination of types of both 

 authors shows that the American shell is more produced and patulous 

 in front and more attenuated and abruptly truncate behind, as well as 

 somewhat more inflated. A European series from nine localities shows 

 some individual variation, but all in a direction away from rather than 

 toward the American type. 



MYSELLA MOLLERI (HolboU) Morch. 

 (Plate LXXXVIII, fig. U.) 



Unnamed bivalve No. 7, Moller, Index Moll. GriJnl., p. 24, 1842. 



Montacuia elcvata Morch, Arctic Man , p. 131, 1875, not of Stimjison, 1851. 



Montacula miilleri " Holboll," MoRCH, Arctic Mau., p. 131, 1875; Riuk's Green- 

 land, p. 411, 1877; (name only). 



Montacuia fcrruginosa var. gronlandica Morch, Forteg. Grcinl., Blodd., p. 19, No. 

 164, 1857; tide Posselt, Consp. FauujB Groul., Moll., p. 75, 1898. 



Montacuia moJleri Posselt, Conspectus Fannie Gronl., Moll., i». 74, 1898; in Meddel. 

 oui Gronl., XXXIII, 1898. 



A. 24. Shell rather large for the group, ovate, white, covered by a 

 profuse wrinkled yellow-brown papery periostracum ; valves only mod- 

 erately convex, inequilateral, the anterior part longer and more fully 

 rounded, base convexly arcuate; beaks low, often eroded; teeth of mod- 

 erate size, the anterior about three times as long as the other in the 

 right valve; pallial scar rather wide and uneven, not sharply dis 

 tinguished from the adductor scars; resilium short, stout, ventrally 

 calcareous. Lon. C.4, alt. 4.8, diam. 3 mm. 



From specimens kindly sent by Jensen, who edited Posselt's pos- 

 thumous Conspectus, I am able to identify this species with the shell 

 called Moniacuta molleri after Holboll's manuscript by Morch. The 

 identification can only take date from 1898, as all the i^revious refer- 

 ences were absolutely without any means of identification. Posselt 

 furnishes the link which connects the name with Moller's unnamed 

 diagnosis. It seems curious that Morch should have listed this species 

 under two distinct specific names, but specimens sent by him to Jef- 

 freys show this to have been the case. 



Specimens from Greenland were identified as Montacnta elevata 

 Stimpson, by Torell and Morch, and are now in the Jeffreys collection. 

 There is also one unnamed from the collection made by Moller and 

 Holboll in Greenland. It is perhai)s the shell to which Hiilboll's manu- 

 script name of impura applies, but I was not able to find any tyjie so- 

 named in the Copenhagen collection. It somewhat resembles the fresh, 

 brown specimens of M. lilamdata Stimpson, but is much larger, with 

 more unequal laminie and a coarse, dirty-looking epidermis over a 

 smooth surface. 



' Brit. Conch., V, 1869, p. 177, pi. 100, fig. 5. 



