162 CEYLON PEARL OYSTER REPORT. 



b. Anterolateral teeth very prominent, reaching as far forward as 

 pseudorostrum, from which they are separated only by a shallow 

 concavity on each side. Dorsal surface of carapace with a 

 longitudinal ridge on the branchial region on each side. 



E. liilgendorfi. 



2. Pseudorostrum not projecting beyond tips of lateral cornua, squarely 



truncate. Anterolateral teeth well denned. Carapace somewhat inflated, 



surface rough and uneven. E. sarsii. 



B. Lateral margins of carapace rounded. 



1. Carapace (of male) about one-fourth of total length and one-fifth longer 



than broad. E. ferox. 



2. Carapace (of male) about one-third of total length, nearly twice as long as 



broad. E. affinis. 



Eocuma taprobanica, n. sp. Plate L, figs. 1 to 20 ; Plate IT., figs. 21 to 28. 



Description of Female, sub-adult, with developing oostegites. Total length,* 

 11-1 millims. (figs. 1, 2, 6): 



The carapace is about two-sevenths of the total length, very broad and flattened, 

 with a well-marked lateral carina on each side. The greatest width is about 

 five-sixths of the length, and is at a distance of less than one-third of the length of 

 the carapace from the front, where are situated the incurved lateral cornua. Behind 

 this the slightly convex sides converge towards the hind margin, where the width is 

 about one-half of that measured across the cornua. The pseudorostrum is prominent, 

 ai*l the tip, as seen from above, is broadly notched. External to it on each side the 

 antero-lateral margin forms a blunt tooth, between which and the lateral cornu the 

 outline is again slightly convex. The dorsal surface, which is slightly arched from 

 before backwards and more strongly so from side to side, presents a faintly marked 

 median keel, becoming more distinct anteriorly, where there is a shallow depression 

 on either side of the cephalic lobe. The sides of the carapace are sharply inflected at 

 the lateral edge, so .that the under surface is nearly flat. A transverse ridge runs 

 from each of the lateral cornua to the lower or free margin of the carapace on the 

 under side. The hinder edge, seen from the side, slopes backwards, forming an 

 oblique angle with the lower and with the lateral margins, which meet at its lower 

 end. The ocular lobe is slightly broader than long, and the ijseudorostral plates meet 

 in front of it for a distance equal to its width. The eye is not pigmented in the 

 specimens examined ; there are three corneal facets, large in size, but indistinctly 

 defined. The surface of the carapace presents a faint and inconspicuous jetting 

 which does not interrupt the minute and regularly reticulate texture of the exo- 

 skeleton. 



The transverse width of the thoracic somites diminishes regularly, tapering down 



* The " total length " given in each case excludes the uropoda. 



