146 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxxii. 



while the two which follow bear the same .sculpture as the adult shell, 

 though less strongly developed. The whorls of the adult jjhell are very 

 strongly tabulately shouldered, the shoulder terminating in a promi- 

 nent compressed keel, which is located at about one-third of the dis- 

 tance between the summit and the base of the columella, anterior to 

 the summit. This keel, which ma}" be known as the peripheral keel, 

 marks the widest part of the turn and overarches the rest. Between 

 this keel and the summit of the succeeding whorl there are two addi- 

 tioaal keels which are a little less strongly developed. The basal one 

 of these (the suprasutural keel) is immediately above the suture, while 

 the other (the median keel) lies half-way between it and the peripheral 

 keel. A fourth keel, which is considerably less developed than any of 

 the three others, is situated on the shoulder, about as far posterior to 

 the peripheral keel as the tirst one below the peripheral keel is anterior 

 to it. Base of the last whorl rather short, well arched, marked by 

 about eight subequal spiral lirations, which are a little more closely 

 spaced and less strongly developed near the umbilical chink than away 

 from it. Aperture irregular, bluish white within, with dark border; 

 outer lip thin, rendered sinuous by the keels; columella slender, con- 

 cavely curved; parietal wall covered with a moderately thick, bluish 

 white callus, which is dark edged and gives the peritreme a complete 

 aspect. Operculum thin, orange colored, with depressed eccentric 

 nucleus and many lines of growth. 



The type, which has lost the first two nepionic turns, has five whorls 

 left, which measure: Altitude, 24.5 mm.; greater diameter, 17.4 mm.; 

 lesser diameter, 15.4 mm. ; aperture, altitude (from the posterior angle 

 to the base of the columella), 11.6 mm.; diameter (at right angles to 

 the last, from the middle keel of the outer lip), 9 mm. 



The present species, while fairly constant as far as general outline 

 is concerned, nevertheless presents considerable variations in sculpture. 

 These variations appear to follow certain definite lines, which will be 

 noted below. It is an interesting fact that in all the gravid specimens 

 examined, the nepionic shells taken from the parent, always had the 

 sculpture of the parent. There are 104 shells wh ich belong to this species, 

 all collected by Major Mearns, in Lake Lanao, Mindanao, Philippine 

 Islands. Eleven of these belong to the tj^pical form, which is entered 

 as Cat. No. 192363, U.S.N.M. 



Form alpha (Plate XI, tig. 8). — Differs from typical lanaonis in 

 having the base smooth. There are six specimens of this form. Cat. 

 No. 192364, U.S.N.M. 



FoTin heta (Plate XI, fig. 2). — Has two slender cords between the 

 peripheral and suprasutural keel, instead of a single median one. 

 There are only two specimens of this type. Cat. No. 192365, U.S.N.M. 



Form gamma (Plate XI, fig. 4). — This lacks the keel on the shoul- 



