402 Dr. \V. T. Caiman on the 



.... in the largest specimen narrower than in the smaller 

 ones. Fig. 8 (pi. i.) represents one of the smaller ones." 

 The figure, however, measures 28 mm. in length of capitulum, 



and as it is stated to be " magnified two diameters," it would 

 correspond exactly in this dimension with the largest of the 

 type-specimens. Its width represents an actual measurement 

 of 8*5 mm., which is considerably greater than that of any of 

 the specimens. It does not seem possible, therefore, to 

 identify this figure with any individual specimen, although 

 in the form of the scutum, and particularly in the angle 

 formed by its basal and occludent margins, it shows a certain 

 similarity to the second in point of size among the type- 

 specimens. This individual, of which the capitulum measures 

 9 mm. in length, is described separately below. • 



The Museum also possesses* the remains of the specimen 

 described and figured by Gruvel, as well as a number of 

 oilier specimens from the same locality (" off coast of Cuba ") 

 which were seen but not examined in detail by him (Gruvel, 

 t. c. p. 159). Some error has crept into Gruvel's measure- 

 ments of his specimen. He gives the length of capitulum as 

 14 mm. and its width as 4. 1 , mm., and his statement that, it is 

 about three times as long as wide has been copied by Pilsbiy, 

 who regards this as the chief character distinguishing the 

 species from his M. subcarinatum. The statement, however, 

 is in conflict with Gruvel's own camera drawing of the outline 

 (J, c. pi. xvii. lig. 9) and with the specimen itself. When 

 ihe valves are placed together the capitulum measures about 

 X'6 mm. by b mm., a proportion which agrees well w'ith 

 Gruvel's drawing. 



Description of Holotype. — Valves covered with a fine 

 nearly colourless cuticle, without seta. 1 . Lines of growth 

 well-marked, with finer concentric ridges between; radial 

 striatiens very line, but distinct.' Scutum (fig. 1, A) twice as 

 long as wide, occludent margin convex, tergal margin 

 straight, carinal margin convex above, deeply concave below, 

 basal margin forming an even curve with occludent margin, 

 with the chord of which it makes a very obtuse angle ; basi- 

 carinal angle acute and recurved. . Ridge from umbo to aptx 

 well-marked, curved, distant from occludent margin except 

 near the ends; ridge from umbo to carino-tergal angle low 

 and rounded but distinct. A small umbonal tooth on inner 

 sui face of both valves and a basal area which is radially and 



* Unfortunately the history of these specimens is incomplete, and the* 

 indications of locality and depth quoted by Gruvel tiom the labels 

 cannot now 1"' i 



