168 Gatlijf and Gabriel: Victorian MoUusca. 



similarly spaced interstices. Two or three intercalating ribs appear. 

 The area occupied by the central third bearing ribs fewer in number, 

 but of greater substance. The shell is further ornamented with about 

 twenty irregularly-parted, fine, concentric lamellae, which are diffi- 

 cult to enumerate, owing to their frequent discontinuity. The un- 

 sculptured portion, generically characteristic, appears in the anterior 

 third, resolving itself into a narrow- beam about the width of two 

 ribs, and two grooves. This divides an antei-ior flank of sixteen ribs 

 from a flank of, approximately, ninety-live to the posterioi. The um- 

 bonal region is marked by an encircling furrow, s.ituated about one- 

 sixth the length of shell ; this discriminates two sets of sculpture, 

 the main ornamental ribs terminating at the furrow ; the umbonal 

 ornament is much finer, assuming more the character of radial threads 

 crossed by numerous and stronger lines of growth. This latter area 

 is lighter in colour, and above the level of the shell, forming a sort 

 of cap. Hinge norniial. Ligament internal, linear. Muscle scars not 

 clearly defined ; pallial impression obscure. Inner margin crenulated 

 by the radial sculpture, which, with the concentrics, may be seen 

 from, within. 



Dimensions of 7'2/pe.— Length, 2.5U; breadth, 1.75; depth, 1.25 mm. 



Locality. — Dredged off Rhyll, Western Port, about 6 fathoms. 

 Type taken alive. 



Obs. — This rare and elegant little species has an Australian ally in 

 M. perstriata, Hedley (P.L.S., N.S.W., 1906, Vol. XXXL, Part .'5, p. 

 472, pi. 36, f. 9, 10), from wliicli it differs in its l>i-oadt-r form, and the 

 peculiar capping of the umbo, this latter feature serving as a useful 

 recognition mark. From its Victorian congeners it is easily distin- 

 guished by the narrow beam. Consistency of shape is not apparent, 

 variation existing as regards depth and Avidth of the convexity. The 

 measurements of our few specimens differ considerably, one valve 

 attaining the dimensions of 3.50 x 2.25 mm. 



Type in Mr. C. J. drabriel's collection. 



EXPLANATION OF PLATE IX. 



Fig. L — Montacuta dromanaensis, sp. nov. Interior, left valve. 



Fig. 2. — Montacuta dromanaensis, sp. nov. Interior, right valve. 



Fig. 3.^ — Montacuta dromanaensis, sp. nov. Exterior. 



Fig. 4r.— Montacuta dromanaensis, sp. nov. Exterior, dorsal view. 



Fig. 5. — Condylocardia chapmani, sp. nov. Interior, left valve. 



Fig. 6. — Condylocardia chapmani, sp. nov. Interior, right valve. 



Fig. 7. — Condylocardia chapmani, sp. nov. Exterior. 



Fig. 8. — Condylocardia chapmani, sp. nov. Exterior, dorsal view. 



Fig. 9. — ^Modiiilaria rhyllensis, sp. nov. Exterior. 



Fig. 10. — Modiolaria rhyllensis, sp. nov. Exterior, dorsal view. 



The figuics are variouslv magrnified. 



