Erythrean Molluscan Fauna. 550 
D. spinosus, Chem., itself a delicately chased little shell, 
takes second rank without doubt; D. obesus, d’Orb., a finely 
decussate species, is also eclipsed ; D. semisulcatus, Hanley, 
from the Indian Ocean, posteriorly similar in its sculpture, 
is anteriorly almost plain, the whole of the surface of our 
species being closely ribbed and spirally sharply sulcate, 
which gives a clear-cut character to the sculpture. The 
ventral margin is beautifully multidenticulate. Posteriorly, 
when the two closed valves are viewed laterally, the double 
row of long spined convergent ribs, with the inner ranks of 
cost armed with shorter spines, form a beautiful heart-shaped 
surface, recalling Cardium (Ctenocardia) hystrix, Wood, in 
miniature. Indeed, after a minute comparison of the other 
species of the genus, to some of which allusion has just been 
made, D. cluthratus, Desh. 1859 (cf Reeve, Conch. Icon., 
Donaa, t. 57), perhaps is the nearest ally; but the character 
of the decussating sculpture is seen, with a lens, to be of 
a different character, and it is more isosceles-shaped than our 
new form. 
Cumingia occatilla*, sp.n. (PI. IX. figs. 7, 7 a.) 
C. testa insequilaterali, protea, ovato-oblonga vel fere rotunda, 
hic postice abbreviata, illic subquadrata, alba, delicata; um- 
bonibus haud prominulis, contiguis, obliquatis, superficie 
omni concentrice tenui-lamellata, lamellis marginem apud ven- 
tralem seepius condensatis, irregularibus, in medio regulariter 
dispositis, interstitiis longitudinaliter delicatissime et arcte 
striatis, speciminibus vetustis spe evanidis, postice compressis, 
intus pagina alba, nitida, margine antico simul ac ventrali pallide 
puniceo hie illic variegato, sinu palliali ad medium ascendente, 
ligamento interno, valvis ambabus dente uno cardinali, simul ac 
fossa elongata, oblique cochleari, prieditis, in dextra quoque 
duobus dentibus lateralibus fortiter instructa. 
Alt. 14, lat. 16, diam. 10 mm. (sp. max.). 
This mollusk doubtless, in common with many other Lep- 
tomye, Thyelle, and Cumingie, inhabits sponges and corals ; 
hence the inequality of form, as protean indeed as any British 
Saxicava. The delicate sculpture is almost identical with 
that of Thyella lamellosa, A. Ad., but the hinge, with un- 
doubted laterals in the right valve, seems more akin to 
Cumingia than to Leptomya, with which genus I had 
essayed at first to connect It. 
The large ligamentary pit is obliquely elongate and spoon- 
shaped, most resembling that of Leptomya, An interesting 
