OF WESTERN SIND. 163 



5. EcHiNOLAMPAS SiNDEJSTSis, var. HEMISPH^RICA, Buncan & Sladen. Plate XXIX, 

 Figs. 11-17. 



On examining a large series of specimens from different localities a considerable 

 amount of variation may be observed. This chiefly affects the proportions of length, 

 breadth, and height ; and, although associated in some instances with other small 

 structural modifications, which separately and at first sight appear striking, we do 

 not, after a careful comparative review of the series, feel justified in regarding them as 

 specifically distinct from the present form. 



A well-marked variety, constant through various phases of growth and in different 

 localities, is characterized in the following manner. The disproportion between the 

 length and breadth is rather less, and the marginal contour is also more truly oval ; the 

 height is greater, the dorsal surface has a more inflated appearance, and when seen in 

 longitudinal profile is almost semicircular, the difference between the curvature of the 

 anterior and posterior slopes being scarcely perceptible. The rounding at the margin 

 is somewhat sharper, which gives the actinal surface a rather flatter appearance ; and 

 this character is further emphasized by the slightly smaller extent of the central 

 depression of the test around the peristome. The bourrelets are, perhaps, rather more 

 prominently developed. The summit of the test is more central, and consequently 

 behind the apical disk. The poriferous zones are broader in relation to the inter- 

 poriferous area. 



Although the majority of the characters here noticed are found in specimens which 

 we regard as the young of the type form oi E. Sindensis, they are remarkably constant 

 in a series of tests of all sizes, the greater number being quite as large as those of 

 E. Sindensis, which present all the characters ascribed to the adult form of the type, 

 and one example being much larger than the average size of that form. If only a 

 small number of examples had been available for study, it is probable that the form 

 would have been regarded as a separate species ; but after studying the material at our 

 disposal we do not at present feel justified in considering this form otherwise than as a 

 well-marked variety of E. Sindensis. In addition to the remarks above made as to the 

 young stages of growth, it may also be observed that examples of the type form occur 

 in which the test is higher than usual, with the dorsal profile approaching the 

 hemispherical outline, and which have the wide poriferous zones characteristic of our 

 variety. 



Young forms. The characters above enumerated are present in a relative degree 

 throughout a series of specimens which range from 40 to 77 millim. in length. A 

 smaller test, 32 millim. in length, which, from its general habit and association, we 

 also place under the variety, approaches a subcylindrical form. The margins are thick 

 and tumid ; the actinal surface tumid, and with no trace of the flatness which ■ cha- 

 racterizes the later stages of growth. Unfortunately the details of this example are 

 badly preserved. A drawing of the specimen is given in Figs. 16 & 17. 



