Jackson: A New Species of Unio. 213 
the museum the name Unio insperatus accompanied the two 
specimens. It is just possible, however, that they were so 
named at a later date. 
These White Nab Unios partake somewhat of the shape 
of Unio kendalli; but are much smaller. Both examples, 
being casts, it is difficult to give a decided opinion before seeing 
further specimens, as the salient characters are far too obscure. 
The same argument will apply equally to the immature forms 
from Haiburn Wyke. Both these forms, therefore, must be 
left in abeyance for the present. 
DESCRIPTION OF THE "NEW SPECIES 
Unio kendallt n. sp. 
(Plate AXLY,.;; figs a to 3). 
External characters :—Shell elongately oblong, tumid ; 
anterior end moderately short, rounded ; posterior end much 
produced, gradually decreasing in tumidity towards the go- 
nium, above which the border is obliquely truncate ; hinge-line 
fairly straight, about two-thirds the maximum length of the 
shell; basal-line curved. Gonial ridge rather indistinct. 
Umbones prominent, not contiguous, placed well forward ; 
umbonal region covered by a number of strong parallel and 
slightly wavy ridges, crossing the growth-lines obliquely. 
Lunule and ligament distinct. Growth-lines well-defined, in 
some specimens very pronounced. 
Internal characters :—Anterior adductor scar fairly deep and 
placed well forward; anterior pedal protractor scar small, 
situated posteriorly and ventrally to the above ; anterior pedal 
retractor scar also small, occupying a position contiguous to the 
anterior adductor impression near its upper margin. Posterior 
adductor impression shallow and hardly noticeable on the cast. 
Pseudocardinal (i.e., antero-lateral) teeth and postero-lateral 
lamellae well-developed. 
Dimensions :—Length, 23 inches ; height, 13 inches ; thick- 
ness, I} inches. 
Geol. Horizon :—Lower Estuarine Series, 27 feet above the 
Dogger. 
Locality :—Saltwick, near Whitby, Yorks. 
Remarks :—The characters on which the above description 
is based are spread over several specimens in various stages 
of preservation. One pair of valves (fig. 2), which are 
gaping, exhibit very clearly the peculiar sculpture adorning 
the umbonal region. The ridges appear to radiate from a 
point just anterior to the umbones and cross the growth-lines 
on the flank at an oblique angle. After passing over the gonial, 
or posterior, ridge they cross the upcurving growth-lines 
almost at right-angles. Here, on this specimen, they become 
rgit June 1. 
