370 PROCEEDINGS OF THE NATIONAL MUSEUM vol.93 



Genus CHELONIBIA Leach 



CHELONIBIA PATULA DENTATA, new subspecies 



Plate 31, Figures 4-13 



Holotype.— U.S.NJM. No. 79409, from Estero de Agiabampo, Sonora, 

 Mexico, April 11, 1940, on Callinectes hellicoms Stimpson. 



Description. — Largest diameter, 18 nun.; height, 7 mm. Steeply 

 conical. Orifice polygonal, large, varying from 63 to 77 percent of 

 the greatest diameter of the shell. Surface white, smooth. 



Radii rather wide, smooth and glossy, very little sunken below the 

 parietes. Summits may he slightly oblique or very oblique, minutely 

 jagged. Edge of outer lamina and recipient furrow minutely but 

 distinctly toothed. Outer lamina of some compartments with one 

 to three oblique ridges and pits, so that the lines of suture become 

 toothed. 



Alae: Summits oblique, edges minutely jagged. 



Compartments: The rostrum is the highest compartment and at 

 the base is about twice the diameter of the carina. The sutures on 

 the internal surface of the rostrum are usually indistinct. The lat- 

 eral compartment is slightly wider than the carinolateral. The com- 

 partments may be irregular in shape, especially if the barnacle is 

 situated on the claws of a crab. 



Sheath: Part formed by radii and alae horizontally grooved; part 

 extending to base as pillars vertically ribbed with base denticulate; 

 intermediate part smooth. 



Inner lamina not well differentiated from sheath. 



Vertical plates or septa: Alternate plates do not reach inner 

 lamina ; basal edges finely denticulate. 



Interspaces between vertical plates filled up at extreme top of 

 compartments; tubular for about two-thirds the height of compart- 

 ments, as alternate vertical plates reach the inner lamina; exposed 

 at base of compartment. 



Opercular valves much smaller than the orifice, the opercular mem- 

 brane attached rather high in the orifice. 



Scutum : Occludent margin only slightly inflected except near basal 

 margin; narrow but deep channel runs close to and parallel with 

 margin from apex to base; not sinuous. Pit for adductor muscle 

 deep. Articular ridge small but prominent, supporting a yellowish, 

 horny membrane, which is attached to the inner part of the tergum. 

 Basal ledge on exterior margin, narrows toward rostral end of 

 scutum. 



Tergum: Scuta] margin wider than carinal edge, curved. Artic- 

 ular furrow wide and deep, receiving horny crest from scutum. 

 Articular ridge represented by slightly raised edge of furrow. 



