HELIX-LABYRINTHUS. 163 



This form and the specimen figured on pi. 39, figs. 87-89 are the 

 extremes in aperture development. 



Chemnitz writes of Das Labyrinth as being extremely rare in his 

 time, and speaks of it as " ein ganz ausnehmendes wundernswiirdiges 

 Kiinststiick, welche nicht leichte Jemand ohne Erstauuen ansehen 

 konne." He had not seen a specimen. 



All of the specimens before me are from various localities on the 

 Isthmus. 



H. PLICATA Born. PI. 63, figs. 1, 2, 3, 4, 5, 7, 8, 9. 



Umbilicate, depressed, about equally convex above and beneath, 

 acutely keeled at the circumference, solid, deep rich chestnut- 

 brown ; surface shining, lightly striate, especially below the sutures, 

 under a lens finely densely granulated all over; spire low, convex, 

 apex plane, first whorl polished, first two whorls smooth, light 

 yellowish ; sutures scarcely impressed ; whorls 5, scarcely convex, 

 moderately increasing, the last wide but becoming narrower on its 

 last third (more or less), abruptly deflexed anteriorly, convex 

 beneath, and constricted behind the peristome, with two short 

 diverging furrows marking the positions of the two basal lip teeth ; 

 immediately above the periphery on its last one-fourth, the whorl is 

 concave, forming a shallow gutter, much less pronounced than in 

 typical .H. labyrinthus ; aperture horizontal, ear-shaped, brown in- 

 side, obstructed by three teeth ; peristome expanded and reflexed 

 all around, continuous, brown or white ; the upper margin of lip is 

 toothless, or bears a small compressed acute denticle remote from the 

 margin, opposite the outer basal tooth ; the basal lip is sinuous, 

 rather thick, with two teeth within, the outer one either rather 

 square or conical, often crenulated on the tip, never so large or 

 plate-like as that of H. labyrinthus, the inner tooth blunt, obtuse ; 

 parietal callous elevated, giving rise in the middle to an elevated 

 arcuate lamella entering the aperture ; umbilicus rather broad, the 

 inner sinuosity of the peristome entering it. 



Alt. 22, diam. maj. 55, min. 47 mill. 



Alt. 16, diam. rnaj. 44, min. 39 mill. 



Alt. 17, diam. maj. 36 &, min. 34 mill. 



Porto Cabello, and Carthagena, Venezuela ; Panama. 



H.plicata BORN, Test. Mus. Cses. Vindob., p. 368 (1780). DES- 

 HAYES, Guerin's Mag. de Zool., 1838, 1. 110. PFEIFFER, in Kiister's 

 Conchyl. Cab., p. 204, t. 104, f. 1-4 ; Monographia Hel. Viv., i, p. 



