MARINE MOLLUSKS — MACGINITIE 175 



Island, the Aleutians, and the Shumagins. Dall's tj^pe lot (USNM 

 333648) of Mysella molleri from Greenland (see pi. 20, fig. 5). Six 

 specimens from Frederikshaab, western Greenland, sent to me by 

 Dr. Thorson (see pi. 20, fig. 1). 



Discussion: The shells have a thick, light brown periostracum. 

 All of them are eroded at the umbos (pi. 20, fig. 9). In the largest 

 shell from Point Barrow (from 328 feet) the erosion extends to the 

 ventral one-fourth of the shell, and at the umbos the erosion is so deep 

 that the tooth is visible from the exterior. This shell is larger and 

 more inflated than the others and the teeth are particularly large and 

 coarse. This specimen contained 24 embryos, with shells about 0.65 

 mm. in length fsee pi. 20, fig. 4). 



In the 4 atypical specimens mentioned above, the umbos (which are 

 eroded as in typical M. planata) are somewhat more centrally located 

 than in typical specimens, the shell appears thinner, and the peri- 

 ostracum seems to be somewhat more wrinkled. In the largest specimen 

 (pi. 20, fig. 7), the only one opened, the hinge teeth are exceptionally 

 small, being about half as large as those of a typical M. planata 

 of comparable size, a character that is compatible with the thinner and 

 less chalky nature of the shell. 



In the synonymy above, the first four references and the sLxth are 

 taken from Dall (1899, p. 891). He states "Posselt furnishes the link 

 which connects the name with Morch's unnamed diagnosis. The iden- 

 tification can take date only from 1898 as all the previous references 

 were absolutely without any means of identification," I have not 

 had access to aU of the literature cited in these references but if Dall's 

 statement is correct, Montacuta molleri Morch must fall as a synonym 

 of Montacuta planata (Dall), for in 1885 Dall described this species as 

 Tellimya planata from some shells from Plover Bay (pi. 20, fig. 3). 

 Although Posselt gave validity to Montacuta molleri by his description 

 in 1898, DaU's description of Tellimya planata was earlier. 



Dall's original description of Tellimya planata (1885a) was accom- 

 panied by a poor outline drawing, apparently by Krause, for Dall 

 later apologized for the illustration and pictured a specimen he had 

 selected for the figured type of Mysella planata (Dall) (1899, pi. 88, 

 fig. 12). The shell he selected is a thin-shelled, small-toothed form 

 in which the umbos are not quite so close to the posterior end (pi. 20, 

 fig. 6) as in his type of M. planata; it resembles the largest of the shells 

 mentioned above from 477 feet from Point Barrow (pi. 20, fig. 7). 

 In the same paper Dall assigned some shells from Greenland (pi. 20, 

 fig. 5) to Mysella molleri (Morch) and selected for the figured tjrpe a 

 typical Montacuta planataP 



'• Call's Rochefortia beringensis and If. grebnitzski belong to the genus Montacuta. The southern range 

 given for Mysella tumida Dall is incorrect— the specimens from off Santa Rosa Island and Monterey Bay 

 belong to two other genera; hence the southern limit for M. tumida is Puget Sound. 



