NO. 1237. SY^'OPSLS OF THE L UCINA CEA—DA LL. 829 



become feebl}^ lamellose on the dorsal areas; hinge, especially the lat- 

 erals, strong', normal; muscular scars as usual; basal margin conspic- 

 uously crenulate. Alt. 6.5, Ion. 6.3, diam. ^.O mm. 



The specimen figured is from the Gulf of California, in i!6 fatlicmis, 

 sand. 



In the region south and east of Lower California this species, which 

 is the Pacific analogue of T*. crenella Dall, is very uniform, ])ut toward 

 the northern extreme of its range the radial riblets on the middle of 

 the disk tend to become obsolete, and then the concentric sculpture is 

 more prominent. This variet}^ does not change its size and never 

 reaches more than one-third the size of the northern tenuismdj)tus^ 

 which had doubtless the same genetic origin, judging from the mate- 

 rial 1 have examined. Very conservative persons might prefer to 

 regard the two as extremes of one poljnnorphic species, but so far I 

 have not found a series which would completely unite them by gentle 

 gradations. 



PHACOIDES (BELLUCINA) CANCELLARIS Philipp 



(Plate XXXIX, fig. 11.) 



This very elegant but hitherto unfigured little shell is now illustrated. 

 It is the Pacific analogue of 1\ wnviantus Dall of the Atlantic coast. 

 The specimen figured is from the Pacific coast of Lower California near 

 the southern end of the peninsula, in 26 fathoms, sand, and measures 

 5.3 mm. in length. It is a shorter shell with fewer ribs than P. 

 amiantwi^ and the nodules on the radials of the posterior dorsal area 

 are longer and more conspicuous. 



DIVARICELLA PERPARVULA, new name. 

 (Plate XXXIX, fig. 8.) 

 This species being unfigured an illustration of it was thought desir- 

 able. The specimen figured is from Acapulco and measures V mm. in 

 length. 



CYRENOIDA FLORIDANA Dall. 

 (Plate XLII, %. 7.) 



This species, hitherto unfigured, is now illustrated. The specimen 

 shown is from a salt pond at Boca Ciega Bay, Florida, and measures 14 

 mm. in length. The average specimens, however, are fully one-half 

 smaller, and are chiefl}" found buried in mossy vegetation in brackish 

 marshes. 



PHACOIDES (PSEUDOMILTHA.?) MEGAMERIS Dall 

 (Plate XLII, fig. 1.) 

 Lncina {PseudomiUhaf) mfgameris Dail, Nautilus, XV, 1901. 

 As this paper is composed of materials toward a monograph of 

 American Lucinacea, it was thought that its interest might be added to 

 by iiTcluding a figure of the largest Lucinoid known, a hitherto unfig- 

 ured species, represented b}' internal casts in the Oligoceue of Claire- 

 mont, St. Anns, Jamaica, West Indies. 



