152 PROCEEDINGS OF THE MALA.COLOGICAL SQCIETT. 



Figs. 8, 9), there is great disparity in the sizes and proportions of the 

 valves, the girdle has a dense covering of blunt spicules, etc. This 

 phylum is represented by C. Burrowi and C. Elioti. In the other 

 phylum, the posterior insertion -plate of valve viii is vertical or thrown 

 forward, the tegmentum projecting behind it (PI. XIV, Figs. 15, 16), 

 the valves are more equal in size and form, and when separated 

 are spaced differently, whilst the girdle spicules are spine-like. 



C. larvceformis is the most differentiated species of this branch, 

 having assumed senile characters in the stage of maturity, while 



C. Gunnii is clearly the least specialized, retaining a less aberrant 

 posterior insertion-plate, and less modified sculpture. These relation- 

 ships may be expressed diagrammatieally thus : — 



The tropical species are the most specialized, the temperate ones 

 the least. 



In the following key the references to proportions or characters of 

 individual valves should be understood to apply to detached valves, 

 not to the portion visible in a perfect specimen. The valves may 

 usually be removed from an alcoholic example without mutilating the 

 girdle or other soft tissues. As each valve is removed it should be 

 numbered, either on the valve itself or, if this be too small, by enclosing 

 each one in a separate vial suitably marked. Neglect of this pre- 

 caution detracts seriously from the value of the material for exact 

 morphological or systematic work. 



Key to the Species of Criptoplax. 



[N.B. — All references to the proportions or characters of individual valves are 

 taken from the detached valves, and apply to the entire valve, not merely the 

 tegmentum.] 



a. Posterior insertion-plate of valve viii projecting backward, the articulamentum 

 projecting behind the tegmentum, the mucro not posterior ; pore-tufts obsolete ; 

 posterior valves widely separated, the greatest space between v and vi. 



b. Valves i and ii only in contact ; iii to viii widely separated, visible through 



inconsiderable orifices, or punctures, in the integument ; the spaces between 



valves iv to viii very wide. C. EHoti, n.sp. 



b\ Valves i to iii in contact, the next one contiguous ; spaces between valves v, 



vi, and vii very wide ; all valves larger thau in the preceding species. 



C. Burrowi, Smith. 

 ff 1 . Posterior insertion -plate of valve viii vertical, or thrown forward, the tegmentum 

 projecting beyond the articulamentum behind, mucro posterior. 



b. Valve ii longer than viii, and valves vi, vii, and viii smaller than iv and v ; 

 v to viii having a median sulcus in place of the dorsal area, and widely 

 separated from one another. Spicules of the girdle very short. 



C. larvceformis, Burr. 



