Notes on the Family Cathypnidfe. By J. Murray. 549 



(figs. 1, Sa, 12, 13, etc.). The dorsal plate rarely also terminates 

 anteriorly in angles or spines (C. luna, M. lunaris, Jf. hamata, etc.). 



The membrane connecting the two plates is usually folded in, 

 making the lateral and posterior sulci (indicated in fig. 1 by 

 dotted lines). A line can be seen running upwards and outwards 

 from the posterior angles of the dorsal plate to the ventral plate. 

 I l}elieve that the ventral plate proper ends at this line. 



The ventral plate, as thus defined, is always shorter than the 

 dorsal ; that is to say, the dorsal projects farther back. 



Some species have no sulcus, the membrane not being folded 

 in, but passing straight across from plate to plate (C. hastata, 

 M. bidla). 



The posterior prolongation, which is seen in almost all the 

 figures as a rounded lobe between the end of the dorsal plate and 

 the toes, is the part that Gosse refers to as a "shelly boss." I 

 refer to it provisionally simply as the '* posterior lobe." Gosse 

 suggests that this part may be the basal joint of the foot, which 

 seems likely enough when we consider the lateral views. 



Underneath this boss is a smaller part, usually considered to be 

 the whole of the foot. It appears to consist of one or two short 

 joints. It bears the toe or toes, which are longer or shorter, 

 straight or curved, shouldered or not. 



The dorsal plate is either quite plain on the surface, or more or 

 less wrinkled or faceted. The faceting is always symmetrical, and 

 is constant for each species. The commonest pattern is that shown 

 in the figure of C. ohioeiisis (fig. 14«). The central markings are 

 irregular hexagons, those towards the margins more obscure. 



Other patterns of facets are found in C. mira (fig. 3), C. nitida, 

 C. signifera (fig. 13rt), C. spinifera (fig. 17), etc. Some are simply 

 sulcate dorsally (figs. 5, 6, 9, etc.). some are wrinkled ((7. flecdlis, 

 etc.). M. turbo (fig. 11a) has peculiar transverse wrinkles. 



The ventral plate has always some wrinkles, usually character- 

 istic for each species. 



In describing a species the chief points to be noted are — the 

 general form ; relative width of dorsal and ventral plates ; depth 

 of sulcus ; form of anterior margins, dorsal and ventral if different, 

 and if bounded by spines ; anterior termination of dorsal lateral 

 margin ; faceting'or not of dorsal plate ; form and prominence of 

 posterior lobe; form of toes, if straight or curved, tapering, 

 shouldered, or clawed ; depth of lorica dorso-ventrally. 



The principal dimensions which should be taken are — total 

 length of contracted lorica, length of dorsal plate, length of toe, 

 breadth of dorsal plate, ventral plate, and of anterior border, angle 

 to angle. 



The dorsal and ventral anterior margins should be distinguished 

 when they differ. What appears to be the dorsal anterior margin 

 usually consists largely of the edge of the connecting membrane. 



