REPORT ON THE LAMELLIBRANCHIATA. 123 



approacli very closely to Vemis calo2'>hyUa. Romer is wrong, in my judgment, in 

 considering figs. 125 and 126 of the Thesaurus as representing Venus tiara. 



Venus (Chione) jacksoni, n. sp. (PI.' III. figs. 2-2e). 



Testa transversim ovata, utrinque aliquanto acuminata, vakle inaequilateralis, medio- 

 criter compressa, lamellis paucis valde distantibus tenuibus hie illic spinosis instmcta, 

 incrementique lineis striata, livido-fuscescens, radiis duobus angustis albis, postice 

 incHnatis, aliis latioribus antice ornata. Margo dorsalis posticus elongatus, late arcuatus, 

 paululum obliquus, anticus longe brevior, valde oblique descendens, levissime concavus. 

 Latus anticum acute rotundatum, posticum inferne productum, magis acuminatum. 

 Margo ventralis late curvatus, postice leviter subsinuatus, intus minute crenulatus. 

 Lunula lauceolata, fuscescens. Dentes cardinales tenues, divergentes. Sinus pallii 

 elongatus, linguseformis. Impressiones museulares parvse, subpjTiformes. Pagina 

 interna fuscopurpurea, versus marginem albida, iu medio radio albo bijjartita. 



The form of this species is irregularly ovate, acuminate at both ends, especially behind. 

 The anterior slope is straightish or a little incurved at the lunule, and much more descend- 

 ing than the hinder dorsal margin. This is broadly curved at first, suljsequently descend- 

 ing more abruptly, and ^\'ith the ventral margin forms a rather acutely rounded angle. 

 The lower edge is widely arcuate in front, but towards the hinder extremity becomes 

 indistinctly sinuated, a feature best seen within the valves. The exterior of the valves 

 is finely striated by the lines of growth, and in addition bears a few very remote con- 

 centric ribs. These are thin and curved over towards the umbones, except where they are 

 produced into spine-like prolongations. These are four iu number upon each rib, erect, 

 hollow above, and situated one above the other so as to form four radiating series, 

 three of them having a posterior inclination and the fourth near the anterior margin. 

 The beaks are rather small, not quite adjacent, and situated at a point which marks off" 

 about three-elevenths of the entire length of the shell from the anterior end. The lunule 

 is narrow, three times as long as wide, of a brown colour, and circumscribed by an 

 impressed stria. The area is somewhat sunken, margined at first by a rounded ridge 

 on each valve which subsequently becomes less apparent. In the right valve the teeth 

 are three in number and rather fine. The hindmost is elongate, diverges from the apex 

 of the umbo, and runs parallel \\dth the ligament. The two others are in the same line 

 with each other, near together, and fall almost perpendicularly from the beak. Parallel 

 with and close to the front marain there is a Ions narrow oroove extending; the length of 

 the lunule which receives the acute edge of the opposite valve. Within the hinder 

 margin, beyond the ligament, there is a similar furrow, also for the reception of the sharp 

 margin of the left valve. In this there are two teeth, the anterior slender, the posterior 



